Configuring DHCP

Dynamic Host Configuration Protocol (DHCP) for IPv4 and IPv6 dynamically assign network configurations to end hosts without statically configure an IP address for each device on the network. However, the underlying architecture and feature sets require different configurations on the switch.

DHCP IPv4

DHCPv4 acts as an extension of the older BOOTP protocol and relies heavily on Layer 2 broadcasts to assign IPv4 addresses to a new IPv4 client on the network. The core mechanism of DHCPv4, also known as DORA, has the following four step transaction:
  1. Discover (Broadcast) - The client sends out messages to 255.255.255.255 looking for DHCP servers on the network.
  2. Offer (Unicast/Broadcast) - A listening DHCP server returns an IPv4 address to the client.
  3. Request (Broadcast) - The client broadcasts an acceptance message to the DHCP server and rejects unselected DHCP servers.
  4. Acknowledge (Unicast/Broadcast) - The DHCP server finalizes the lease and sends the client a subnet mask, gateway, and DNS servers.
DHCPv4 has the following key features:
  • Option 82 (Relay Agent Information) - Allows intermediates switches to inject their physical port data (Circuit ID) into the client broadcast messages before forwarding the message to a central DHCP server.
  • Granular Options - Relies on highly specific integer options including Option 43 for Vendor-specific data such as Wireless Controller IPs, Option 150 for TFTP servers, and Option 67 for bootfiles.
  • Default Gateway Assignment - The DHCP server provides the client with a default gateway (Option 3).

DHCP IPv6

DHCPv6 eliminates broadcast traffic and operates over IPv6 Multicast and works with ICMPv6 Neighbor Discovery. Instead of DORA, DHCPv6 uses a four step transaction targeting specific multicast groups, such as ff02::1:2, the All-DHCP-Relay-Agents-and-Servers address:
  1. Solicit (Multicast) - The client sends messages on the network looking for a server.
  2. Advertise (Unicast) - The server indicates availability and preference.
  3. Request (Unicast) - The client requests specific parameters from the selected server.
  4. Reply (Unicast) - The server confirms the lease and configuration.
DHCPv6 has the following key features:
  • Router Advertisements (RA) Dependency - A DHCPv6 client does not send a Solicit message unless a local router first sends an ICMPv6 RA with the M-Flag, Managed Configuration, or O-Flag, Other Configuration, set to 1. The router dictates how the client receives an IP address.
  • Stateless vs. Stateful
    • Stateful (M-Flag) - The DHCPv6 server tracks leases and hands out the actual IPv6 addresses.
    • Stateless (O-Flag)- The client uses Stateless Address Autoconfiguration (SLAAC) to generate an IPv6 address and only uses the DHCPv6 server to obtain extra details such as DNS servers or domain names.
  • Prefix Delegation (DHCPv6-PD) - A downstream router requests an entire routed subnet prefix from an upstream ISP server to assign to local VLANs.
  • Unified URIs (Option 59) - DHCPv6 does not use legacy options such as separating TFTP IPs and filenames in favor of consolidated URL strings.

Key Architectural Differences

Feature DHCPv4 DHCPv6
Transport Protocol UDP Ports 67 (Server) and 68 (Client) UDP Ports 547 (Server) and 546 (Client)
Initial Discovery Layer 2 Broadcast (255.255.255.255) Layer 3 Multicast (ff02::1:2)
Default Gateway Provided by the DHCP Server Provided by ICMPv6 Router Advertisements
Lease Tracking Always Stateful Can be Stateful and Stateless
Hardware ID Relies on the physical MAC Address Relies on a generated DUID (DHCP Unique Identifier)

DHCP Server

The router with DHCP Server enabled acts as a server that allocates and delivers network addresses with desired configuration parameters to its hosts.

The DHCP server is based on ISC Kea.

The router with an DHCP Server enabled acts as a server that allocates and delivers network addresses with desired configuration parameters to its hosts.

DHCP Server support includes:

DHCPv4 support includes:
  • Configurable on different interfaces - Routed, VLAN, LAG, Sub-interface, and LAG Sub-interface.
  • Configurable lease time for allocated network addresses.
  • Configurable DNS domain.
  • Configurable DNS servers.
  • Configurable subnets with parameters:
    • Default gateway
    • DNS servers
    • Ranges
    • Lease time

Additional features for DHCP include the following:
  • Configurable TFTP server
  • Configurable TFTP bootfile

Additional features for DHCP includes the following:
  • Configurable Vendor options with sub options
  • Configurable suboption types including IPv4 address, array of IPv4 addresses, and string
  • TFTP bootfile now supports an URI

Additional features for DHCP include a configurable static IP address for exclusive use by a given client, based on the client’s MAC address.

Example deployment:

DHCP Server on an aggregation switch, via VXLAN tunnels.



Configuring DHCP Servers

Global DHCP server options are configured per address family and apply to all subnets. Access the commands in the DHCP Server Configuration Mode.

To enter the DHCP server global configuration mode, use the following commands:

switch# configure
switch(config)# dhcp server
switch(config-dhcp-server)#

To disable the DHCP server:

switch(config-dhcp-server)# disabled

Use the following commands to configure the DNS servers. Only two servers can be configured globally per address family.

switch(config-dhcp-server)# dns server ipv4 192.0.2.4 192.0.2.5
switch(config-dhcp-server)# dns server ipv6 2001:db8:0:10::53 2001:db8:0:10::5353

The following commands configure the domain names for allocated IP addresses. For example, add a domain with the name podV4.example.com for DHCPv4 and a domain with the name podV6.example.com for DHCPv6.

switch(config-dhcp-server)# dns domain name ipv4 podV4.example.com
switch(config-dhcp-server)# dns domain name ipv6 podV6.example.com

The following commands configure lease time for the allocated IP addresses. For example, configure the lease time as one (1) day.

switch(config-dhcp-server)# lease time ipv4 1 days 0 hours 0 minutes
switch(config-dhcp-server)# lease time ipv6 1 days 0 hours 0 minutes

The following command configures the TFTP Server-Name. The server can be in the form of either an IPv4 or IPv6 address or a fully qualified domain name. For example, configure the TFTP server with the IPv4 address, 192.0.2.6 and an TFTP server with the IPv6 address, 2601:600:cb02:d070:14b7:6ad0:bedb:ef3:

switch(config-dhcp-server)# tftp server option 66 ipv4 192.0.2.6

The following command configures the TFTP Servers. 

switch(config-dhcp-server)# tftp server option 150 ipv4 192.0.2.6 192.0.2.7

The following command configures the TFTP Server Bootfile-Name for IPv4 and IPv6: 

switch(config-dhcp-server)# tftp server file ipv4 bootfile.conf
switch(config-dhcp-server)# tftp server file ipv6 bootfile.conf

The following command configures Vendor specific option. To enter the Vendor Option Configuration Mode from the DHCP Server Configuration mode, specify a vendor class identifier, only available in DHCPv4. For example, Vendor option for clients with vendor class identifier vendorClassIDA.

switch(config-dhcp-server)# vendor-option ipv4 vendorClassIDA

The following command configures default. If you do not configure the default, the DHCP Server sends the configured Vendor option to clients requesting a Vendor option with a vendor class identifier that does not match any configured Vendor option.

switch(config-dhcp-server)# vendor-option ipv4 default

The following command configures suboptions for the Vendor. The configuration sends the resulting Vendor option in a hexadecimal format to the desired client. The output displays aVendor option with a suboption with IPv4 address 192.0.2.8, for clients with the vendor class identifier vendorClassIDA, resulting in Vendor option 1:4:c0:0:2:8.

Sub option number is 1
Length of the Data is 4
Data is c0:0:2:8
dhcp server
vendor-option ipv4 vendorClassIDA
sub-option 1 type ipv4-address data 192.0.2.8

The following command configures the Vendor option with IPv4 addresses 192.0.2.8 and 192.0.2.9, for clients with the vendor class identifier vendorClassIDA, resulting in the Vendor option fe:8:c0:0:2:8:c0:0:2:9.

switch(config-dhcp-server)# vendor-option ipv4 vendorClassIDA sub-option 254 type array ipv4-address data 192.0.2.8 192.0.2.9

The following command configures Vendor option with a string “vendor”, for all clients whose vendor class identifier does not match any configured Vendor option, resulting in Vendor option 1e:3:46:4f:4f..

switch(config-dhcp-server)# vendor-option ipv4 default sub-option 30 type string data "vendor"

The following command sets up Vendor option holding two suboptions, suboption 1 holds the IPv4 address 192.0.2.8, and suboption 2 holds a string “vendor”, for all clients whose vendor class identifier does not match any configured Vendor option, resulting in Vendor option 1:4:c0:0:2:8:2:3:46:4f:4f.

switch(config-dhcp-server)# vendor-option ipv4 default sub-option 1 type ipv4-address data 192.0.2.8 sub-option 2 type string data “vendor"

Configuring DHCP Server Subnets

DHCP Server settings can also be configured per subnet and overrides the DHCP Server global mode configurations. There can be multiple subnets configured, but they must not overlap. EOS disables overlapping subnets.

The following command enters DHCP Server subnet mode under the IPv4 address family.

switch# config
switch(config)# dhcp server 
switch(config-dhcp-server)# subnet 192.0.2.0/32

The following command configures the name of the subnet. For example, name subnetv4 for DHCPv4.

switch(config-dhcp-subnet-ipv4)# name subnetv4

The following command configures range of IP addresses of the subnet. The range must be within the subnet mask, otherwise the subnet becomes disabled.

switch(config-dhcp-subnet-ipv4)# range 192.0.2.100 192.0.2.199

The following command configures the DNS servers for a subnet. Configure up to 2 servers per subnet.

switch(config-dhcp-subnet-ipv4-range)# dns server 192.0.2.1 192.0.2.10

The following command configures the lease time for allocated IP addresses of the subnet.
switch(config-dhcp-subnet-ipv4)# lease time ipv4 3 days 0 hours 0 minutes

The following command configures the default-gateway for a subnet. 
switch(config-dhcp-server)# subnet 192.0.2.0/32
switch(config-dhcp-subnet-ipv4)# default-gateway 192.0.2.3

The following command configures the TFTP Server-Name for a subnet. The server can be in the form of either an IPv4 address or a fully qualified domain name, but can only be configured for DHCPv4.
switch(config-dhcp-subnet-ipv4)# tftp server option 66 subnet-tftp.example.com

The following command configures a list of TFTP servers. The server can only be in the form of an IP address, but can only be configured for DHCPv4.
switch(config-dhcp-subnet-ipv4)# tftp server option 150 192.0.2.6 192.0.2.7

The following command configures the TFTP server Bootfile-Name for a subnet, but can only be configured for DHCPv4.
switch(config-dhcp-subnet-ipv4)# tftp server file subnet-bootfile.conf

Example DHCP Server Subnets Configuration
switch# config
switch(config)# dhcp server 
switch(config-dhcp-server)# subnet 192.0.2.0/32
switch(config-dhcp-subnet-ipv4)# name subnetv4
switch(config-dhcp-subnet-ipv4)# range 192.0.2.100 192.0.2.199
switch(config-dhcp-subnet-ipv4-range)# dns server 192.0.2.1 192.0.2.10
switch(config-dhcp-subnet-ipv4)# lease time ipv4 3 days 0 hours 0 minutes 
switch(config-dhcp-server)# subnet 192.0.2.0/32
switch(config-dhcp-subnet-ipv4)# default-gateway 192.0.2.3
switch(config-dhcp-subnet-ipv4)# tftp server option 66 subnet-tftp.example.com
switch(config-dhcp-subnet-ipv4)# tftp server option 150 192.0.2.6 192.0.2.7
switch(config-dhcp-subnet-ipv4)# tftp server file subnet-bootfile.conf
The following command configures a static IP address for exclusive use by a client. Enter the DHCP Server Subnet Configuration Mode, (config-dhcp-mac-address-ipv4) from and specify the client MAC Address. The IP address must not be used by another client. Only DHCPv4 addresses allowed for this configuration. 
switch(config-dhcp-subnet-ipv4)# reservations 
switch(config-dhcp-sub-v4-reserve)# mac-address 1a1b.1c1d.1e1f
switch(config-dhcp-sub-v4-rsrv-mac-address)# ipv4-address 192.0.2.0

Displaying DHCP Information

Show DHCP Server Information

The following command displays the DHCP Server information.

switch# show dhcp server ipv4
IPv4 DHCP Server is active
Debug log is enabled
DNS server(s): 192.0.2.4 192.0.2.5
DNS domain name: podV4.example.com
Lease duration: 1 days 0 hours 0 minutes
TFTP server: 192.0.2.6 (Option 66)
192.0.2.6 192.0.2.7 (Option 150)
TFTP file: https://该邮件地址已受到反垃圾邮件插件保护。要显示它需要在浏览器中启用 JavaScript。:123/example/one
Active Leases: 1
IPv4 DHCP interface status:
Interface   Status
-------------------------------------------------
Ethernet1   Inactive (Could not determine VRF)
Ethernet2   Inactive (Not in default VRF)
Ethernet3   Inactive (Kernel interface not created yet)
Ethernet4   Inactive (Not up)
Ethernet5   Inactive (No IP address)
Ethernet6   Inactive (No Link Local address)
Ethernet7   Inactive (DHCP relay is configured for this interface)
Ethernet8   Inactive (DHCP relay is always on)
Ethernet9   Active

Vendor information:
Vendor ID: default
Sub-options         Data       
---------------- ----------------
1          192.0.2.0
2          “vendor”

Vendor ID: vendorClassIDA
Sub-options       Data       
---------------- --------------------
254        192.0.2.8, 192.0.2.9

Subnet: 192.0.2.0/24
Subnet name: subnetFooV4
Range: 192.0.2.100 to 192.0.2.199
DNS server(s): 192.0.2.1 192.0.2.10
Lease duration: 3 days 0 hours 0 minutes
Default gateway address: 192.0.2.3
TFTP server:
 subnet-tftp.example.com (Option 66)
 192.0.2.6 192.0.2.7 (Option 150)
 TFTP boot file: subnet-bootfile.conf
 Active leases: 1
 Reservations:
 MAC address: 1a1b.1c1d.1e1f
 IPv4 address: 192.0.2.201
 MAC address: 2a2b.2c2d.2e2f    
 IPv4 address: 192.0.2.150

Displaying Disabled Subnets

When a subnet becomes disabled, the show dhcp server [ipv4|ipv6] output displays the disabled message under Disabled reason(s). None of the disabled subnets have active leases. Currently, the output displays only 2 disabled reasons. 

switch# show dhcp server
IPv4 DHCP Server is active
DNS server(s): 10.2.2.2
Lease duration: 1 days 0 hours 0 minutes
Active Leases: 0
IPv4 DHCP interface status:
Interface   Status
-------------------------------------------------
Ethernet1   Active

Subnet: 10.0.0.0/24 (Subnet is disabled)
Range: 10.0.0.1 to 10.0.0.10
DNS server(s): 10.3.3.3 10.4.4.4
Default gateway address: 10.0.0.4
Active leases: 0
Disabled reason(s):
Overlapping subnets: 10.0.0.0/8 

Subnet: 10.0.0.0/8 (Subnet is disabled)
Range: 10.0.0.1 to 10.0.0.10
DNS server(s): 10.5.5.5
Default gateway address: 10.0.0.3
Active leases: 0
Disabled reason(s):
Overlapping subnets: 10.0.0.0/24 

For Overlapping ranges:
switch# show dhcp server
IPv4 DHCP Server is active
DNS server(s): 10.2.2.2
Lease duration: 1 days 0 hours 0 minutes
Active Leases: 0
IPv4 DHCP interface status:
Interface   Status
-------------------------------------------------
Ethernet1   Active

Subnet: 10.0.0.0/8 (Subnet is disabled)
Range: 10.0.0.1 to 10.0.0.10
Range: 10.0.0.9 to 10.0.0.12
DNS server(s): 10.3.3.3 10.4.4.4
Default gateway address: 10.0.0.4
Active leases: 0
Disabled reason(s):
Overlapping range: 10.0.0.9 to 10.0.0.12 

E.g. Duplicate static IP address reservation:
Subnet: 10.0.0.0/8 (Subnet is disabled)
Subnet name:
Range: 10.0.0.1 to 10.0.0.10
DNS server(s): 10.5.5.5
Default gateway address: 10.0.0.3
Active leases: 0
Reservations:
MAC address: 1a1b.1c1d.1e1f    
IPv4 address: 10.0.0.11

MAC address: 2a2b.2c2d.2e2f    
IPv4 address: 10.0.0.11

Disabled reason(s):
Duplicate IPv4 address reservation: 10.0.0.11

For DHCPv6, Direct and Relay indicates that the DHCP Server accepts broadcast and relayed messages.

switch# show dhcp server ipv6
IPv6 DHCP server is active
Debug log is enabled     
DNS server(s): fe80::6     
DNS domain name: aristanetworks.example.com        
Lease duration: 1 days 3 hours 30 minutes      
Active leases: 0               
IPv6 DHCP interface status:    
Interface    Status         
--------------- ------         
Ethernet1    Active
Ethernet3    Active        

Subnet: fe80::/10      
Subnet name: foo     
Range: fe80::1 to fe80::3
DNS server(s): fe80::4 fe80::5          
Direct: Inactive (Multiple interfaces match this subnet: Ethernet1 Ethernet3)
Relay: Active            
Active leases: 0

For DHCPv6, a subnet may match only one interface and vice versa. Otherwise the subnet is disabled and no lease assigned for that subnet.

interface Ethernet1
no switchport
ipv6 address 2001:db8:0:10::1/64
dhcp server ipv6
interface Ethernet3
no switchport
ipv6 address 2001:db8:0:11::1/64
dhcp server ipv6
dhcp server
subnet 2001:db8::/56

The following enables DHCPv6 on Ethernet1 (with address fc00::1/7 and fe80::1/10), and then configures subnets fc00::/7 and fe80::/64 for DHCPv6.

interface Ethernet1
no switchport
ipv6 address fc00::1/7
ipv6 address fe80::1/64 link-local 
dhcp server ipv6
dhcp server
subnet fc00::/7
subnet fe80::/64

#show dhcp server ipv6
IPv6 DHCP server is active     
DNS server(s):  fc00::2     
DNS domain name: aristanetworks.example.com        
Lease duration: 1 days 3 hours 30 minutes      
Active leases: 0               
IPv6 DHCP interface status:    
Interface    Status         
--------------- ------         
Ethernet1    Active        

Subnet: fc00::/7      
Subnet name: foo               
Range: fc00::1 to fc00::5       
DNS server(s): fc00::6 fc00::8          
Direct: Inactive (This and other subnets match interface Ethernet1)
Relay: Active

Active leases: 0

Subnet: fe80::/64      
Subnet name: subnetBarV6         
Direct: Inactive (This and other subnets match interface Ethernet1)
Relay: Active

Active leases: 0

Leases

The following output displays the IP addresses allocated by the DHCP Server with the show dhcp server [ipv4|ipv6] leases command. It also displays the expected end time for the address, the time when the address is assigned, and the equivalent MAC address.

switch# show dhcp server leases
10.0.0.10
End: 2019/06/20 17:44:34 UTC
Last transaction: 2019/06/19 17:44:34 UTC
MAC address: 5692.4c67.460a

2000:0:0:40::b 
End: 2019/06/20 18:06:33 UTC   
Last transaction: 2019/06/20 14:36:33 UTC      
MAC address: 165a.a86d.ffac

DHCP Server Show Commands

Use the show dhcp server command to display DHCP server information.
  • DHCPv4 display example:
    switch# show dhcp server ipv4
IPv4 DHCP Server is active
Debug log is enabled
DNS server(s): 10.2.2.2
DNS domain name: domainFoo
Lease duration: 1 days 0 hours 0 minutes
TFTP server:
serverFoo (Option 66)
10.0.0.3 (Option 150)
TFTP file: fileFoo
Active Leases: 1
IPv4 DHCP interface status:
   Interface   Status
-------------------------------------------------
   Ethernet1   Inactive (Could not determine VRF)
   Ethernet2   Inactive (Not in default VRF)
   Ethernet3   Inactive (Kernel interface not created yet)
   Ethernet4   Inactive (Not up)
   Ethernet5   Inactive (No IP address)
   Ethernet6   Active

Vendor information:
Vendor ID: default
  Sub-options         Data       
---------------- ----------------
      1          192.0.2.0, 192.0.2.1

Vendor ID: vendorFoo
  Sub-options       Data       
---------------- -----------
      2            192.0.2.2
      3            “Foo”

Subnet: 10.0.0.0/8
Subnet name: subnetFoo
Range: 10.0.0.1 to 10.0.0.10
DNS server(s): 10.1.1.1 10.2.2.2
Lease duration: 3 days 3 hours 3 minutes
Default gateway address: 10.0.0.3
TFTP server:
subnetServerFoo (Option 66)
10.0.0.4 (Option 150)
TFTP boot file: subnetFileFoo
Active leases: 1
Reservations:
MAC address: 1a1b.1c1d.1e1f
IPv4 address: 10.0.0.1

MAC address: 2a2b.2c2d.2e2f    
IPv4 address: 10.0.0.2

  • For DHCPv6, there are two additional fields in subnet information output, Direct field and the Relay field. These two fields specify if the DHCP Server is accepting broadcast or relayed messages.

    The Direct field displays Active when the subnet matches the interface with DHCPv6 configured. This indicates the server is accepting broadcast messages.

    The Direct field displays Inactive when there is another existing subnet already matching the interface, or when the subnet matches more than one DHCP configured interface.

    Examples of outputs for the DHCPv6 show dhcp server command:

    In this example, DHCPv6 is configured with subnet fe80::/10 while being enabled on Ethernet1 with address fe80::1/64 and on Ethernet3 with address fe80::2/64.
    switch# show dhcp server ipv6
IPv6 DHCP server is active
Debug log is enabled                                                                                                                                                                                                                     
DNS server(s): fe80::6                                                                                                                                                                                                                     
DNS domain name: testaristanetworks.com                                                                                                                                                                                                        
Lease duration: 1 days 3 hours 30 minutes                                                                                                                                                                                                      
Active leases: 0                                                                                                                                                                                                                               
IPv6 DHCP interface status:                                                                                                                                                                                                                    
   Interface    Status                                                                                                                                                                                                                         
--------------- ------                                                                                                                                                                                                                         
   Ethernet1    Active
   Ethernet3    Active                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                               
Subnet: fe80::/10                                                                                                                                                                                                                      
Subnet name: foo                                                                                                                                                                                                                                                                                                                                                                                                                                     
Range: fe80::1 to fe80::3
DNS server(s): fe80::4 fe80::5                                                                                                                                                                                                                                                                                                                                                                                                                                          
Direct: Inactive (Multiple interfaces match this subnet: Ethernet1 Ethernet3)
Relay: Active                                                                                                                                                                                                                            
Active leases: 0

  • This example illustrates when multiple subnets match an interface. In this example, DHCPv6 is configured with subnets fc00::/7 and fe80::/10 while being enabled on Ethernet1 with address fe80::1/10 and fc00::1/7.
    switch# show dhcp server ipv6
IPv6 DHCP server is active                                                                                                                                                                                                                     
DNS server(s):  fc00::2                                                                                                                                                                                                                     
DNS domain name: testaristanetworks.com                                                                                                                                                                                                        
Lease duration: 1 days 3 hours 30 minutes                                                                                                                                                                                                      
Active leases: 0                                                                                                                                                                                                                               
IPv6 DHCP interface status:                                                                                                                                                                                                                    
   Interface    Status                                                                                                                                                                                                                         
--------------- ------                                                                                                                                                                                                                         
   Ethernet1    Active                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                               
Subnet: fc00::/7                                                                                                                                                                                                                      
Subnet name: foo                                                                                                                                                                                                                               
Range: fc00::1 to fc00::5                                                                                                                                                                                                       
DNS server(s): fc00::6 fc00::8                                                                                                                                                                                                                                                                                                                                                                                                                                          
Direct: Inactive (This and other subnets match interface Ethernet1)
Relay: Active
                                                                                                                                                                                                                                  
Active leases: 0

Subnet: fe80::/10                                                                                                                                                                                                                      
Subnet name: bar                                                                                                                                                                                                                                                                                                                                                                                                                                         
Direct: Inactive (This and other subnets match interface Ethernet1)
Relay: Active
                                                                                                                                                                                                                                  
Active leases: 0

  • When disabled, the show dhcp server command displays the disable message with a reason. The number of active leases of the disabled subnets will be 0. In this example, there are overlapping subnets.
    switch# show dhcp server
IPv4 DHCP Server is active
DNS server(s): 10.2.2.2
Lease duration: 1 days 0 hours 0 minutes
Active Leases: 0
IPv4 DHCP interface status:
   Interface   Status
-------------------------------------------------
   Ethernet1   Active

Subnet: 10.0.0.0/24 (Subnet is disabled - overlapping subnet 10.0.0.0/8)
Range: 10.0.0.1 to 10.0.0.10
DNS server(s): 10.3.3.3 10.4.4.4
Default gateway address: 10.0.0.4
Active leases: 0

Subnet: 10.0.0.0/8 (Subnet is disabled - overlapping subnet 10.0.0.0/24)
DNS server(s):
Default gateway address: 10.0.0.3
Active leases: 0

  • In this example, the display output shows overlapping ranges.
    switch# show dhcp server
IPv4 DHCP Server is active
DNS server(s): 10.2.2.2
Lease duration: 1 days 0 hours 0 minutes
Active Leases: 0
IPv4 DHCP interface status:
   Interface   Status
-------------------------------------------------
   Ethernet1   Active

Subnet: 10.0.0.0/8 (Subnet is disabled - range 10.0.0.9-10.0.0.12 overlaps with an existing pool)
Range: 10.0.0.1 to 10.0.0.10
Range: 10.0.0.9 to 10.0.0.12
DNS server(s): 10.3.3.3 10.4.4.4
Default gateway address: 10.0.0.4
Active leases: 0

  • This example shows duplicate static IP address reservation.
    Subnet: 10.0.0.0/8 (Subnet is disabled - ipv4-address 10.0.0.11 is reserved more than once)
Subnet name:
DNS server(s):
Default gateway address: 10.0.0.3
Active leases: 0
Reservations:
MAC address: 1a1b.1c1d.1e1f    
IPv4 address: 10.0.0.11

MAC address: 2a2b.2c2d.2e2f    
IPv4 address: 10.0.0.11

  • Use the show dhcp server leases command to display detailed information about the IP addresses allocated by the DHCP Server (including the IP address, the expected end time for that address, the time when the address is handed out, and the equivalent MAC address).
    switch# show dhcp server leases
10.0.0.10
End: 2019/06/20 17:44:34 UTC
Last transaction: 2019/06/19 17:44:34 UTC
MAC address: 5692.4c67.460a

2000:0:0:40::b                                                                                                                                                                                                                                
End: 2019/06/20 18:06:33 UTC                                                                                                                                                                                                                   
Last transaction: 2019/06/20 14:36:33 UTC                                                                                                                                                                                                      
MAC address: 165a.a86d.ffac

DHCP Relay Global Configuration Mode

Configure DHCP Relay using the dhcp relay command in the global configuration mode. The command places the switch in DHCP Relay mode and allows the configuration of DHCP Relay on several interfaces with a single command. The configuration entered in the DHCP Relay global configuration mode can be overridden by equivalent interface specific commands.

Examples

The dhcp relay command places the switch in the DHCP Relay configuration mode.
switch(config)# dhcp relay
switch(config-dhcp-relay)#

Specify the IP address of the default DHCP or DHCPv6 Server. Multiple IP addresses can be specified and DHCP requests forward to all specified helper addresses. Configure an ip helper-address IP_Address under each desired routing interface.

Use the following commands to forward DHCP broadcast packets received on interface Ethernet1 and Vlan2 to DHCP servers at 10.0.0.1, 10.0.0.2, and to hostname DefaultDHCPHostname:
switch(config)# interface ethernet1
switch(config-if-Et1)# no switchport
switch(config-if-Et1)# ip address 192.168.1.1/16
 
switch(config)# interface vlan2
switch(config-if-Et1)# ip address 172.16.1.1/16
 
switch(config)# dhcp relay
switch(config-dhcp-relay)# server 10.0.0.1
switch(config-dhcp-relay)# server 10.0.0.2
switch(config-dhcp-relay)# server DefaultDHCPHostname

Use the following commands to forward DHCPv6 broadcast packets received on interface ethernet1 to a DHCPv6 Server at fc00::3.
switch(config)# interface ethernet1                     
switch(config-if-Et1)# no switchport                        
switch(config-if-Et1)# ipv6 address fc00::1/10 
 
switch(config)# dhcp relay
switch(config-dhcp-relay)# server fc00::3

The configuration points a routed interface to the specified DHCP and DHCPv6 server, if the configuration meets following criteria:
  • The default VRF contains the routed interface.
  • The interface has an IP address configured.
  • The configuration does not occur on a Management or a Loopback interface.

Use the following commands to remove the default DHCPv4 or DHCPv6 Server.
switch(config)# dhcp relay
switch(config-dhcp-relay)# no server 10.0.0.1
switch(config-dhcp-relay)# no server 10.0.0.2
switch(config-dhcp-relay)# no server DefaultDHCPHostname
switch(config-dhcp-relay)# no server fc00::3

To override the default DHCP Server on an interface, the parameter,ip helper-addressIP_Address, must be used.

Use the following commands to forward a DHCP broadcast packet received on interface Ethernet1 to DHCP Servers at 10.0.0.1, 10.0.0.2 and hostname DefaultDHCPHostname, but VLAN2 broadcasts packets to the DHCP Server at 10.0.0.3 only.
switch(config)# interface ethernet 1
switch(config-if-Et1)# no switchport
switch(config-if-Et1)# ip address 192.168.1.1/16
 
switch(config)# interface vlan2
switch(config-if-Et1)# ip address 172.16.1.1/16
switch(config-if-Et1)# ip helper-address 10.0.0.3
 
switch(config)# dhcp relay
switch(config-dhcp-relay)# server 10.0.0.1
switch(config-dhcp-relay)# server 10.0.0.2
switch(config-dhcp-relay)# server DefaultDHCPHostname

To override the default DHCPv6 Server on an interface, the parameter, ipv6 helper-address IPv6_Address> must be used.

Use the following commands to forward a DHCPv6 broadcast packet received on interface Ethernet1 to DHCPv6 Server at fc00::3, and VLAN2 broadcasts packets to DHCPv6 Server at fc00::4 only.
switch(config)# interface ethernet 1
switch(config-if-Et1)# no switchport
switch(config-if-Et1)# ipv6 address fc00::1/10
 
switch(config)# interface vlan2
switch(config-if-Et1)# ipv6 address fc00::2/10
switch(config-if-Et1)# ipv6 helper-address fc00::4
 
switch(config)# dhcp relay
switch(config-dhcp-relay)# server fc00::3

Configure DHCP Relay for IPv4 unnumbered interfaces by adding a DHCP IPv4 helper address and configuring the vendor option.

Use the information option command to enter DHCP Relay Information Option Configuration Mode:
switch(config)# dhcp relay
switch(config-dhcp-relay)# information option
switch(config-information-option)# vendor-option

Configure Option-37 in DHCPv6 Relay to include the host name of the switch along with MAC address and interface name in the remote id of the option. It requires the remote-id format to be specified in the configuration mode.

Use the following command to add the remote-id:
switch(config)# ipv6 dhcp relay option remote-id format %m:%h:%p

You can disable DHCP or DHCPv6 Relay functionality from a specific interface. This disables both DHCP Relay global and interface mode configurations.

Use the following command to disable DHCP Relay functionality only.
switch(config)# interface vlan3
switch(config-if-Et1)# dhcp relay ipv4 disabled

Use the following to disable DHCPv6 Relay functionality only.
switch(config)# interface vlan3
switch(config-if-Et1)# dhcp relay ipv6 disabled

Displaying DHCP Relay

The show ip dhcp relay command displays all the interfaces enabled with DHCP Relay and the server configured on these interfaces.

Example
switch# show ip dhcp relay
DHCP Relay is active
DHCP Relay Option 82 is disabled
DHCPv6 Relay Link-layer Address Option (79) is disabled
DHCPv6 Relay Remote ID (Option 37) encoding format: MAC address:interface ID
DHCP Smart Relay is disabled
Default L3 interface DHCP servers:   
  DHCPv4 servers: 10.0.0.1
                  10.0.0.2
                  DefaultDHCPHostname 
  DHCPv6 servers: fc00::3
Interface: Ethernet1
  DHCP Smart Relay is disabled
  DHCPv6 all subnet relaying is disabled 
  Using default DHCPv4 servers        
  Using default DHCPv6 servers
Interface: Ethernet2                  
  DHCP Smart Relay is disabled         
  DHCPv6 all subnet relaying is disabled
  Using default DHCPv4 servers        
  DHCPv6 servers: fc00::4
Interface: Vlan2                   
  DHCP Smart Relay is disabled         
  DHCPv6 all subnet relaying is disabled
  DHCPv4 servers: 11.0.0.3       
  DHCPv6 servers: fc00::4 
Interface: Vlan3           
  DHCP Smart Relay is disabled         
  DHCPv6 all subnet relaying is disabled
  DHCPv4 Relay is disabled            
  DHCPv6 Relay is disabled

Use the show ip dhcp relay command to display DHCP Relay for unnumbered interfaces: 
switch# show ip dhcp relay
   DHCP Relay Option (82) is enabled
   DHCP Relay vendor-specific suboption (9) under information option (82)

DHCP Relay Across VRF

The EOS DHCP relay agent supports forwarding of DHCP requests to DHCP servers located in a different VRF to the DHCP client interface VRF. In order to enable VRF support for the DHCP relay agent, Option 82 (DHCP Relay Agent Information Option) must first be enabled. The DHCP relay agent uses Option 82 to pass client specific information to the DHCP server.

These sections describe DHCP Relay across VRF features:
The DHCP relay agent inserts Option 82 information into the DHCP forwarded request, which requires the DHCP server belongs to a network on an interface, and that interface belongs to a different VRF than the DHCP client interface. Option 82 information includes the following:

  • VPN identifier - The VRF name for the ingress interface of the DHCP request, inserted as sub-option 151.

    Table 1. VPN Identifier
    SubOpt Len ASCII VRF Identifier
    151 7 V R F N A M E

  • Link selection - The subnet address of the interface that receives the DHCP request, inserted as sub-option 5. After enabling the DHCP smart relay, the link selection fills with the subnet of the active address. The relay agent sets the Gateway IP address (gIPaddr) to its IP address so that DHCP messages can be routed over the network to the DHCP server.
    Table 2. Link Selection
    SubOpt Len Subnet IP Address
    5 4 A1 A2 A3 A4

  • Server identifier override - The primary IP address of the interface that receives the DHCP request, inserted as sub-option 11. After enabling the DHCP smart relay, the server identifier fills with the active address, one of the primary or secondary addresses chosen by smart relay mechanism.
    Table 3. Link Selection
    SubOpt Len Overriding Server Identifier Address
    11 4 B1 B2 B3 B4

  • VSS control suboption as suboption 152 - The DHCP server strips out this suboption when sending the response to the relay, indicating that the DHCP server used VPN information to allocate IP address.
  • Circuit ID - Identifies the circuit, interface or VLAN, on the switch that received the request.
  • Remote ID - Identifies the remote host.

Note: The DHCP server must be capable of handling VPN identifier information in Option 82.

Direct communication between DHCP client and server may not be possible if they reside in separate VRFs. The Server identifier override and Link Selection sub-options set the relay agent to act as the DHCP server, and enable all DHCP communication to flow through the relay agent.

The relay agent adds all the appropriate sub-options, and forwards all request packets, including renew and release,to the DHCP server. When the relay receives the DHCP server response messages, EOS removes Option 82 information and forwards the response to the DHCP client in the client VRF.

Configuring DHCP Relay

EOS inserts the DHCP relay agent information option into DHCP messages relayed to the DHCP server. The ip helper-address command enables DHCP relay on an interface and relays DHCP messages to the specified IPv4 address.

Example

This command enables DHCP relay on the interface ethernet 1/2; and relays DHCP messages to the server at 1.1.1.1.
switch(config)# interface ethernet 1/2
switch(config-if-Et1/2)# ip helper-address 1.1.1.1
switch(config-if-Et1/2)#

The commands provided in the following examples enable the attachment of VRF-related tags in the relay agent information option. If both the DHCP client interface and server interface exist on the same VRF, default or non-default, then EOS does not insert the VRF-related DHCP relay agent information option.

Examples
  • This command configures the DHCP relay to add option 82 information.
    switch(config)# ip dhcp relay information option

  • These commands configures two new VRF instances and assign them Route Distinguishers (RDs).
    switch(config)# vrf instance mtxxg-vrf
switch(config-vrf-mtxxg-vrf)# router bgp 50
switch(config-router-bgp)# vrf mtxxg-vrf
switch(config-router-bgp-vrf-mtxxg-vrf)# rd 5546:5546
switch(config)# vrf instance qchyh-vrf
switch(config-vrf-qchyh-vrf)# router bgp 50
switch(config-router-bgp)# vrf qchyh-vrf
switch(config-router-bgp-vrf-qchyh-vrf)# rd 218:218

  • This command configures an interface connected to DHCP client in vrf mtxxg-vrf and assigns an IP address.
    switch(config)# interface ethernet 9
switch(config-if-Et9)# no switchport

  • This command configures the DHCP client interface in VRF mtxxg-vrf.
    switch(config-if-Et9)# vrf mtxxg-vrf
switch(config-if-Et9)# ip address 10.10.0.1/16

  • This command configures the server interface in VRF qchyh-vrf.
    switch(config-if-Et11)# vrf qchyh-vrf
switch(config-if-Et11)# ip address 10.40.0.1/16

  • This command configures a helper address for a DHCP server in VRF qchyh-vrf.
    switch(config-if-Et11)# ip helper-address 10.40.2.3 vrf qchyh-vrf

Configuring Option 82

Use the following commands to enter Information Option (Option 82) insertion and configure the format of information options:

switch(config)# dhcp relay
switch(config-dhcp-relay)# information option
switch(config-information-option)#

To specify the format for the circuit-id encoding, use the following command:

switch(config-information-option)# circuit-id encoding (%x | %p)

The default format uses string denoted by %p. Setting the encoding to %x enables hex encoding for the circuit ID. The configured value must be a valid hex number. If not configured, DHCP Relay uses the default format.

To specify the format for the remote-id encoding, use the following command:

switch(config-information-option)# remote-id encoding (%x | %p)

The default format uses string denoted by %p. Setting the encoding to %x enables hex encoding for the remote ID. The configured value must be a valid hex number. If not configured, DHCP Relay uses the default format.

DHCP Relay Global Configuration Mode Show Command

Example

This command displays the VRF specifier for the server:
switch# show ip dhcp relay
DHCP Relay is active
DHCP Relay Option 82 is enabled
DHCP Smart Relay is disabled
Interface: Ethernet9
Option 82 Circuit ID: Ethernet9
DHCP Smart Relay is disabled
DHCP servers: 10.40.2.3
10.40.2.3:vrf=qchyh-vrf

DHCP Relay in VXLAN EVPN

The ip dhcp relay information option (Global) command enables the configuration of the DHCP server to uniquely identify the origin of the request using a source-interface and the helper address. Configure the source interface with a routable address used by the DHCP server to uniquely identify the DHCP relay agent that forwarded the client request.

Configuring DHCP Relay in VXLAN EVPN (IPv4)

Use the following command to enable the DHCP relay information option (Option 82) required to specify a source interface. 

switch(config)# ip dhcp relay information option

The following configures a Loopback interface as the source interface. 

switch(config)# interface Loopback1
switch(config-if-Lo1)# ip address 1.1.1.1/24

Use the following commands to configure the Loopback interface as the specified source interface for the helper address. 

switch(config)# interface vlan100
switch(config-if-Vl100)# ip helper-address 10.1.1.4 source-interface Loopback1

Use the following commands to configure the Loopback interface when the DHCP server resides in a different VRF (red). The source interface must be configured in the DHCP server VRF for the command to take effect. 

switch(config)# interface Loopback3
switch(config-if-Lo3)# vrf red
switch(config-if-Lo3)# ip address 1.1.1.1/24

switch(config)# interface vlan100
switch(config-if-Vl100)# ip helper-address 10.1.1.4 vrf red source-interface Loopback3

The following command disables the use of source interface along with the helper address. 

switch(config)# interface vlan100
switch(config-if-Vl100)# no ip helper-address 10.1.1.4 source-interface Loopback1

Configuring DHCP Relay in VXLAN EVPN (IPv6)

Use the following commands to configure a local interface.

switch(config)# interface Loopback2
switch(config-if-Vl100)# ipv6 address 2001::10:20:30:1/128

Use the following commands to configure the Loopback interface as the local interface for the helper address. 

switch(config)# interface vlan200
switch(config-if-Vl200)# ipv6 dhcp relay destination 2002::10:20:30:2 local-interface Loopback2

Use the following commands to configure the Loopback interface when the DHCP server is in a different VRF (red). The local interface must be configured in the DHCP server's VRF for the command to take effect. 

switch(config)# interface Loopback4
switch(config-if-Lo4)# vrf red
switch(config-if-Lo4)# ipv6 address 2001::10:20:30:1/128

switch(config)# interface vlan200
switch(config-if-Vl200)# ipv6 dhcp relay destination 2002::10:20:30:2 vrf red local-interface Loopback4

Use the following command to disable the use of local interface along with the helper address. 

switch(config-if-Vl200)# no ipv6 dhcp relay destination 2002::10:20:30:2 local-interface Loopback4

The following command displays the status of DHCP relay option (Option 82) and lists the configured DHCP servers. 

switch# show ip dhcp relay
DHCP Relay is active
DHCP Relay Option 82 is enabled
DHCP Smart Relay is disabled
Interface: Vlan100
  Option 82 Circuit ID: Vlan100
  DHCP Smart Relay is disabled
  DHCP servers: 10.1.1.4
Interface: Vlan200
  Option 82 Circuit ID: Vlan100
  DHCP Smart Relay is disabled
  DHCP servers: 2002::10:20:30:2

DHCP Relay Agent for IPv6

Configuring IPv6 DHCP Relay

  • Configuring the IPv6 DHCP Relay Agent (Global)
  • Configuring DHCP for IPv6 Relay Agent
  • Configuring the Client Link Layer Address for the IPv6 DHCP Relay Agent
  • Configuring DHCPv6 Relay for Option 37
  • Clearing IPv6 DHCP Relay Counters

Configuring the IPv6 DHCP Relay Agent (Global)

The ipv6 dhcp relay always-on command enables the switch DHCP IPv6 Relay Agent globally regardless of the DHCP IPv6 Relay Agent status on any interface. EOS enables DHCP IPv6 Relay Agent by default if at least one routable interface has an ipv6 dhcp relay destination statement.

Example

This command enables the DHCP relay agent.
switch(config)# ipv6 dhcp relay always-on
switch(config)#

Configuring DHCP for IPv6 Relay Agent

The ipv6 dhcp relay destination command enables the DHCP IPv6 Relay Agent function and specifies the client message destination address on an interface.

Example

This command enables the DHCP IPv6 Relay Agent function and sets the client message destination address to 2001:0db8:0:1::1 on interface ethernet 4.
switch(config)# interface ethernet 4
switch(config-if-Et4)# ipv6 dhcp relay destination 2001:0db8:0:1::1
switch(config-if-Et4)

Configuring DHCPv6 Relay for Option 37

The DHCPv6 Relay Option 37 allows a DHCPv6 relay agent to insert a Remote-ID option (Option 37) into DHCPv6 messages. This option provides the DHCPv6 server with information about the client's location, such as the MAC address of the relay agent, the ingress interface, and the VLAN ID. This is useful for network administrators to track the origin of DHCP requests and to enforce policies based on the client's location.

Use the following command to specify using the MAC address, hostname, and interface name for the Remote-ID:
switch(config)# ipv6 dhcp relay option remote-id format %m:%h:%p
Displaying the Remote-ID Configuration Information

Use the show ip dhcp relay command to display the Option 37 configuration:

switch# show ip dhcp relay
DHCP relay is active
DHCPv6 relay remote ID option (37) encoding format: MAC address:hostname:interface name

Clearing IPv6 DHCP Relay Counters

The clear ipv6 dhcp relay counters command resets the DHCP relay counters. The configuration mode determines which counters to reset:
  • Global configuratio: - Clears the counters for the switch and for all interfaces.
  • Interface configuration - Clears the counter for the configuration mode interface.

Examples
  • These commands clear all DHCP relay counters on the switch.
    switch(config-if-Et4)# exit
switch(config)# clear ipv6 dhcp relay counters
switch(config)#

  • These commands clear the DHCP relay counters for interface ethernet 4.
    switch(config)# interface ethernet 4
switch(config-if-Et4)# clear ipv6 dhcp relay counters
switch(config)#

Displaying IPv6 DHCP Relay Information

  • IPv6 DHCP Relay Status
  • IPv6 DHCP Relay Counters

IPv6 DHCP Relay Status

The show ip dhcp relay command displays the status of DHCP relay agent parameters on the switch and each interface where at least one feature parameter is listed. The command displays the status for both global and interface configurations.

Example

This command displays the DHCP Agent Relay parameter status.
switch(config)# interface ethernet 1/2
switch(config-if-Et1/2)# show ip dhcp relay
DHCP Relay is active
DHCP Relay Option 82 is disabled
DHCPv6 Relay Link-layer Address Option (79) is disabled
DHCP Smart Relay is disabled
Interface: Ethernet1/2
  DHCP Smart Relay is disabled
  DHCP servers: 1::1
                2001:db8:0:1::1
switch(config-if-Et1/2)#

IPv6 DHCP Relay Counters

The show ipv6 dhcp relay counters command displays the number of DHCP packets received, forwarded, or dropped on the switch and on all interfaces enabled as DHCP relay agents.

Example

This command displays the IP DHCP relay counter table.
switch> show ipv6 dhcp relay counters

          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop |         Last Cleared
----------|----- ---- -----|---------------------
  All Req |  376  376    0 | 4 days, 19:55:12 ago
 All Resp |  277  277    0 |
          |                |
Ethernet4 |  207  148    0 | 4 days, 19:54:24 ago

switch>

DHCP Snooping with Bridging

In this configuration, in addition to sending DHCP packets to relay after adding information option, the packets can also bridge within the VLAN. In the bridging mode, the switch intercepts DHCP packets, inserts option-82 if not already present, and bridges the packet within the VLAN. This mode of DHCP snooping can be configured without DHCP relay configuration.
Note: EOS supports DHCP Snooping with Bridging on MLAG configurations.

Configuring DHCP Snooping with Bridging

Following are the steps to configure DHCP snooping with bridging:
  1. Enable DHCP snooping feature using the ip dhcp snooping command.
    switch# ip dhcp snooping

  2. Enable the insertion of option-82 in DHCP request packets using the ip dhcp snooping information option command. By default, option-82 is disabled and must be enabled for DHCP Snooping to be functional.
    switch# ip dhcp snooping information option

  3. Enable DHCP snooping on the corresponding VLANs using the ip dhcp snooping vlan command. By default,EOS disables DHCP snooping on any VLAN.
    switch# ip dhcp snooping vlan

  4. Set the circuit-id information sent in option-82. By default, EOS sends the Interface name and VLAN ID. Remote circuit-id contains the MAC address of the relay agent.
    switch# ip dhcp snooping information option circuit-id type 2 format
%h:%p  Hostname and interface name
%p:%v  Interface name and VLAN ID

  5. Enable bridging capabilities of DHCP snooping using the ip dhcp snooping bridging command. This command enables DHCP snooping with or without DHCP relay configuration.
    switch# ip dhcp snooping bridging

Configuring IPv6 DHCP Snooping

Enabling IPv6 DHCP Snooping

The ipv6 dhcp snooping command enables DHCP snooping globally on the switch. DHCP snooping provides a Layer 2 feature that can be configured on LAN switches. Arista switches support Option-37 insertion that allows relay agents to provide remote-ID information in DHCP request packets.

Note: DHCPv6 VLAN classification and DHCPv4 VLAN classification share same hardware resource.

Examples
  • The following configuration enables the IPv6 DHCP snooping feature at the global level.
    switch(config)# ipv6 dhcp snooping
switch(config)# ipv6 dhcp snooping remote-id option
switch(config)# ipv6 dhcp snooping vlan <vlan|vlan-range>

  • The following commands display the IPv6 DHCP snooping state.
    switch(config)# ipv6 dhcp snooping
switch(config)# show ipv6 dhcp snooping
DHCPv6 Snooping is enabled
DHCPv6 Snooping is operational
DHCPv6 Snooping is configured on following VLANs:
  2789-2790
DHCPv6 Snooping is operational on following VLANs:
  2789
Insertion of Option-37 is enabled

DHCP Snooping with Bridging Show Commands

The show dhcp snooping displays the DHCP snooping with bridging information.
switch# show ip dhcp snooping
DHCP Snooping is enabled
DHCP Snooping is operational
DHCP Snooping is configured on following VLANs:
 650
DHCP Snooping bridging is operational on following VLANs:
 650
Insertion of Option-82 is enabled
 Circuit-id sub-option Type: 0
 Circuit-id format: Interface name:Vlan ID
 Remote-id: 00:1c:73:8d:eb:67 (Switch MAC)

Troubleshooting

  • Configure all the needed commands to enable DHCP snooping and operational on all the VLANs.

  • show ip dhcp snooping displays the DHCP snooping status.

  • show ip dhcp snooping counters displays dropped snooped packets.

  • show ip dhcp snooping counters debug displays the reason for dropped packets.
    
switch# show ip dhcp snooping counters debug
Counter                           Requests          Responses
----------------------------- ----------------- -----------------
Received                                      3                 2
Forwarded                                     3                 2
Dropped - Invalid VlanId                      0                 0
Dropped - Parse error                         0                 0
Dropped - Invalid Dhcp Optype                 0                 0
Dropped - Invalid Info Option                 0                 0
Dropped - Snooping disabled                   0                 0

  • Check if the packets are hitting the TCAM rule. 
    switch# show platform trident tcam detail | grep -i dhcp
DHCP Snooping uses 3 entries.
…
655402               45 hits - DHCP client to relay trap-to-cpu

DHCP Commands

DHCP Server Commands

IPv4 DHCP Snooping Commands

IPv4 DHCP Relay Commands

IPv6 DHCP Relay Commands

IPv6 DHCP Snooping Commands

clear ip dhcp relay counters

The clear ip dhcp relay counters command resets the DHCP relay counters. The configuration mode determines which counters are reset:.

The Interface configuration command clears the counter for the configuration mode interface.

Command Mode

Privileged EXEC

Command Syntax

clear ip dhcp relay counters [interface_name]

Parameters

interface_name - Specify the interface to clear counters.. Add the following options:
  • no parameter - Clears counters for the switch and for all interfaces.
  • interface ethernet e_num - Clears counters for the specified Ethernet interface.
  • interface loopback l_num - Clears counters for the specified loopback interface.
  • interface port-channel p_num - Clears counters for the specified port-channel Interface.
  • interface vlan v_num  -Clears counters for the specified VLAN interface.

Examples
  • These commands clear the DHCP relay counters for vlan 1045 and shows the counters before and after the clear command.
    switch# show ip dhcp relay counters

          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop |         Last Cleared
----------|----- ---- -----|---------------------
  All Req |  376  376    0 | 4 days, 19:55:12 ago
 All Resp |  277  277    0 |
          |                |
 Vlan1001 |  207  148    0 | 4 days, 19:54:24 ago
 Vlan1045 |  376  277    0 | 4 days, 19:54:24 ago

switch# clear ip dhcp relay counters interface vlan 1045

          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop |         Last Cleared
----------|----- ---- -----|---------------------
  All Req |  380  380    0 | 4 days, 21:19:17 ago
 All Resp |  281  281    0 |
          |                |
 Vlan1000 |  207  148    0 | 4 days, 21:18:30 ago
 Vlan1045 |    0    0    0 |          0:00:07 ago

  • These commands clear all DHCP relay counters on the switch.
    switch(config-if-Vl1045)# exit
switch(config)# clear ip dhcp relay counters
switch(config)# show ip dhcp relay counters

          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop | Last Cleared
----------|----- ---- -----|-------------
  All Req |    0    0    0 |  0:00:03 ago
 All Resp |    0    0    0 |
          |                |
 Vlan1000 |    0    0    0 |  0:00:03 ago
 Vlan1045 |    0    0    0 |  0:00:03 ago

clear ip dhcp snooping counters

The clear ip dhcp snooping counters command resets the DHCP snooping packet counters.

Command Mode

Privileged EXEC

Command Syntax

clear ip dhcp snooping counters [counter_type]

Parameters

counter_type  - Specify the type of counter to reset. Options include the following:
  • no parameter - Counters for each VLAN.
  • debug - Aggregate counters and drop cause counters.

Examples
  • This command clears the DHCP snooping counters for each VLAN.
    switch# clear ip dhcp snooping counters
switch# show ip dhcp snooping counters

     | Dhcp Request Pkts | Dhcp Reply Pkts |
Vlan |  Rcvd  Fwdd  Drop | Rcvd Fwdd  Drop | Last Cleared
-----|------ ----- ------|----- ---- ------|-------------
 100 |     0     0     0 |    0    0     0 |  0:00:10 ago

switch#

  • This command clears the aggregate DHCP snooping counters.
    switch# clear ip dhcp snooping counters debug
switch# show ip dhcp snooping counters debug

Counter                       Snooping to Relay Relay to Snooping
----------------------------- ----------------- -----------------
Received                                      0                 0
Forwarded                                     0                 0
Dropped - Invalid VlanId                      0                 0
Dropped - Parse error                         0                 0
Dropped - Invalid Dhcp Optype                 0                 0
Dropped - Invalid Info Option                 0                 0
Dropped - Snooping disabled                   0                 0

Last Cleared:  0:00:08 ago

switch#

clear ipv6 neighbors

The clear ipv6 neighbors command removes the specified dynamic IPv6 neighbor discovery cache entries. Commands that do not specify an IPv6 address remove all dynamic entries for the listed interface. Commands that do not specify an interface remove all dynamic entries.

Command Mode

Privileged EXEC

Command Syntax

clear ipv6 neighbors [port][dynamic_ipv6]

Parameters
  • port Interface through which neighbor is accessed. Options include the following:
    • no parameter - Removes all dynamic entries.
    • interface ethernet e_num - Specify the Ethernet interface by e_num.
    • interface loopback l_num  - Specify the Loopback interface by l_num.
    • interface port-channel p_num  - Specify the Port-channel interface by p_num p_num.
    • interface vlan v_num - Specify the VLAN interface by v_num.
  • dynamic_ipv6 - Specifies the address of entry to remove. Options include the following:
    • no parameter - Removes all dynamic entries for specified interface.
    • ipv6_addr - Removes the IPv6 address of the entry.

Example

This command removes all dynamic neighbor entries for vlan 200.
switch# clear ipv6 neighbors vlan 200
switch#

clear ipv6 dhcp relay counters

The clear ipv6 dhcp relay counters command resets the DHCP relay counters. If you do not specify a port, the command clears the counters for the switch and for all interfaces. Otherwise, the command clears the counter for the specified interface.

Command Mode

Privileged EXEC

Command Syntax

clear ipv6 dhcp relay counters [port]

Parameters

port - Specify the interface to access the neighbor. Options include the following:
  • no parameter - Removes all dynamic entries.
  • interface ethernet e_num - Specify the Ethernet interface by e_num.
  • interface loopback l_num  - Specify the Loopback interface by l_num.
  • interface port-channel p_num  - Specify the Port-channel interface by p_num p_num.
  • interface vlan v_num - Specify the VLAN interface by v_num.

Example

These commands clear the DHCP relay counters for interface ethernet 4 and shows the counters before and after the clear command.
switch(config)# show ipv6 dhcp relay counters

          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop |         Last Cleared
----------|----- ---- -----|---------------------
  All Req |  376  376    0 | 4 days, 19:55:12 ago
 All Resp |  277  277    0 |
          |                |
Ethernet4 |  207  148    0 | 4 days, 19:54:24 ago


switch(config)# interface ethernet 4
switch(config-if-Et4)# clear ipv6 dhcp relay counters

          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop |         Last Cleared
----------|----- ---- -----|---------------------
  All Req |  380  380    0 | 4 days, 21:19:17 ago
 All Resp |  281  281    0 |
          |                |
Ethernet4 |    0    0    0 |4 days, 21:18:30 ago
These commands clear all DHCP relay counters on the switch.
switch(config-if-Et4)# exit

switch(config)# clear ipv6 dhcp relay counters

switch(config)# show ipv6 dhcp relay counters
          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop | Last Cleared
----------|----- ---- -----|-------------
  All Req |    0    0    0 |  0:00:03 ago
 All Resp |    0    0    0 |
          |                |
Ethernet4 |    0    0    0 | 0:00:03 ago
switch(config)#

clear ipv6 dhcp snooping counters

The clear ipv6 dhcp snooping counters command resets the DHCP snooping packet counters.

Command Mode

Privileged EXEC

Command Syntax

clear ipv6 dhcp snooping counters [counter_type]

Parameters
  • counter_type - Specifies the type of counter to reset.
  • no parameter - Clears the counters for each VLAN.

  • debug - Clears aggregate counters and drop cause counters.

Examples
  • This command clears the number of DHCP packets sent and received on each VLAN.
    switch# clear ipv6 dhcp snooping counters
switch# show ipv6 dhcp snooping counters

     | Dhcpv6 Request Pkts | Dhcpv6 Reply Pkts | 
Vlan |  Rcvd   Fwdd   Drop |  Rcvd  Fwdd  Drop | Last Cleared
-----|------ ------ -------|------ ----- ------|------------- 
2789 |     1      1      0 |     1     1     0 |  0:03:09 ago

  • This command clears the number of DHCP packets sent on the switch.
    switch# clear ipv6 dhcp snooping counters debug
switch# show ipv6 dhcp snooping counters debug

Counter                       Snooping to Relay Relay to Snooping
----------------------------- ----------------- -----------------
Received                                      1                 1
Forwarded                                     1                 1
Dropped - Invalid VlanId                      0                 0
Dropped - Parse error                         0                 0
Dropped - Invalid Dhcp Optype                 0                 0
Dropped - Invalid Remote-ID Option            0                 0
Dropped - Snooping disabled                   0                 0

Last Cleared:  0:04:29 ago

default-gateway

The default-gateway command in DHCP Server Subnet Configuration Mode populates DHCP Option 3 (Router Option) in the DHCP payload sent from the switch to the client and allows communication to another VLAN or network.

The [no | default] versions of the command disable the feature and remove the configuration from the running-config.

Command Mode

DHCP Server IPv4 Subnet Configuration

Command Syntax

default-gateway

no default-gateway

default default-gateway

Parameters

  • default-gateway ipv4_address - Add a default gateway to the subnet.

Example

Use the following commands to add the default-gateway, 10.10.10.1, to subnet 172.16.23.11/32:

switch(config)# dhcp server
switch(config-dhcp-server)# subnet 172.16.23.11/32
switchconfig-dhcp-subnet-ipv4)# default-gateway 10.10.10.1
switchconfig-dhcp-subnet-ipv4)#

default-gateway

The default-gateway command in DHCP Server Subnet Configuration Mode populates DHCP Option 3 (Router Option) in the DHCP payload sent from the switch to the client and allows communication to another VLAN or network.

The [no | default] versions of the command disable the feature and remove the configuration from the running-config.

Command Mode

DHCP Server IPv6 Subnet Configuration

Command Syntax

default-gateway

no default-gateway

default default-gateway

Parameters

  • default-gateway ipv6_address

Example

Use the following commands to add the default-gateway, 2001:db8:cafe:a100::99, to subnet 2001:db8:acad:1::fe21/32:

switch(config)# dhcp server
switch(config-dhcp-server)# subnet 2001:db8:acad:1::fe21/32
switchconfig-dhcp-subnet-ipv6)# default-gateway 2001:db8:cafe:a100::99
switchconfig-dhcp-subnet-ipv6)#

dhcp relay

The dhcp relay command places the switch in the DHCP relay mode. Execute this command in the Global Configuration Mode.

The no dhcp relay command removes DHCP relay configuration from the running-config.

Command Mode

Global Configuration Mode

Command Syntax

dhcp relay

no dhcp relay

Example

The dhcp relay command places the switch in the DHCP relay configuration mode.
switch(config)# dhcp relay
switch(config-dhcp-relay)#

dhcp relay ipv6

The dhcp relay ipv6 command in the DHCP Relay Configuration Mode configures DHCP Relay IPv6 routes and disable DHCP route persistence or synchronize neighbors.

Command Mode

DHCP Relay Configuration

Command Syntax

dhcp relay ipv6 routes [persistence disable] | [sync neighbor [ ipv4 | ipv6]

no dhcp relay ipv6

default dhcp relay ipv6

Parameters

  • persistence disable - Configure DHCP client requests settings.
  • sync neighbor [ ipv4 | ipv6] - Configure these settings to retain the DHCP server ID in a request.

Examples

Use the following commands to disable the DHCP IPv6 route persistence:

switch(config)# dhcp relay
switch(config-dhcp-relay)# ipv6 routes persistence disabled
switch(config-dhcp-relay)#

Use the following commands to synchronize with neighbor, 172.16.23.15:

switch(config)# dhcp relay
switch(config-dhcp-relay)# sync neighbor 172.16.23.15
switch(config-dhcp-relay)#

client requests

The client requests command in the DHCP Relay Configuration Mode configures DHCP Relay to evaluate incoming.

Command Mode

DHCP Relay Configuration

Command Syntax

client requests [[cross-vrf server-id preserve] | [flooding suppress]]

no client requests

default client requests

Parameters

  • client requests - Configure DHCP client requests settings.
  • cross-vrf server-id preserve - Configure these settings to retain the DHCP server ID in a request.
  • flooding suppress - Configure these settings to prevent flooding DHCP request packets on the network.

Examples

Use the following commands to preserve the DHCP server ID:

switch(config)# dhcp relay
switch(config-dhcp-relay)# client requests cross-vrf server-id preserve
switch(config-dhcp-relay)#

Use the following commands to suppress DHCP request flooding on the network:

switch(config)# dhcp relay
switch(config-dhcp-relay)# client requests flooding suppress
switch(config-dhcp-relay)#

dhcp server

The dhcp server command places the switch in the DHCP relay mode. Execute this command in the DHCP Server Configuration Mode.

The no dhcp server command removes DHCP relay configuration from the running-config.

Command Mode

Global Configuration Mode

Command Syntax

dhcp server

no dhcp server

Example

The dhcp server command places the switch in the DHCP relay configuration mode.
switch(config)# dhcp server
switch(config-dhcp-server)#

dhcp server client

The dhcp server client command in the IPv4 or IPv6 Subnet Configuration Mode configures client options for the DHCP server. Execute this command under the dhcp server configuration mode.

Command Mode

DHCP Server Configuration

DHCP Server Subnet Configuration

DHCP Server IPv4 or IPv6 Subnet Range Configuration

Command Syntax

dhcp server client class [ipv4|ipv6] definition client_class assignments [default-gateway|dns|lease|option|private-option|tftp]

Parameters

  • [ipv4|ipv6] - Select the IP address family.
  • definition client_class - Add a class for the client definition.
  • default-gateway - Configure the client class default gateway sent to DHCP clients.
  • dns - Configure the client class DNS.
  • lease - Configure the client class lease.
  • option - Configure the client class DHCP options.
  • private-option - Configure the client class's private options.
  • tftp - Configure the client class's TFTP options.

Example

Use the dhcp server client class default-gateway command to add a client definition for the IPv4 DHCP client class default gateway of 10.0.0.1. options.
switch(config-dhcp-server)# client class ipv4 definition test1 default-gateway 10.0.0.1

dhcp server debug

The dhcp server debug log command configures DHCP server debugging configuration. Execute this command in the DHCP Server Configuration Mode.

Command Mode

DHCP Server Configuration Mode

Command Syntax

dhcp server debug log file

Parameters

log file - Specify the file location to store debugging logs.

Example

Use the dhcp server log command to add a file location for debugging logs. 
switch(config-dhcp-server)#debug log

dhcp server dns

The dhcp server dns command configures DHCP server DNS options. Execute this command in the DHCP Server Configuration Mode and DHCP Server IPv4 Subnet Configuration Mode.

Command Mode

DHCP Server Configuration

DHCP Server IPv4 or IPv6 Subnet Configuration

Command Syntax

dhcp server dns [domain name domain_name ] [server [ipv4|ipv6] ip_address

Parameters

  • domain name domain_name - Specify the domain name of the DNS server.
  • server [ipv4|ipv6] ip_address - Specify the DNS server as IPv4 or IPv6 and the IP address of the server.

Example

Use the dhcp server dns command to add an IPv4 DNS server, 192.168.10.5, to the DHCP configuration. options.
switch(config-dhcp-server)# dns server ipv4 192.168.10.5

dhcp server lease

The dhcp server lease command configures DHCP server lease options. Execute this command in the DHCP Server Configuration Mode and DHCP Server IPv4 Subnet Configuration Mode.

Command Mode

DHCP Server Configuration

DHCP Server IPv4 or IPv6 Subnet Configuration

Command Syntax

dhcp server lease time [ipv4|ipv6] days days hourshours minutesminutes

Parameters

  • [ipv4|ipv6] - Configure the lease for IPv4 or IPv6.
  • days days - Specify the number of days for the lease to be in effect from 0 to 2000 days.
  • hourshours - Specify the number of hours for the lease to be in effect from 0 to 23 hours.
  • minutesminutes - Specify the number of minutes for the lease to be in effect from 0 to 59 minutes.

Example

Use the dhcp server lease command to add an IPv4 lease to be in effect for 10 days, to the DHCP configuration. 
switch(config-dhcp-server)# dns lease time ipv4 10 days

dhcp server next-server

The dhcp server next-server command in the DHCP Server Configuration Mode populates a specific legacy field in the DHCP packet header called the siaddr, Server IP address. During initialization, a switch requires information about the location of a DHCP server. After receiving an IP address for the bootstrap process, the switch contacts the TFTP or HTTP server and downloads the configuration file specified in the bootfile command.

Command Mode

DHCP Server Configuration

Command Syntax

next-server ipv4_address

no next-server

Parameters

  • next-server ipv4_address - Specify the IPv4 address for the DHCP server.

Example

Use the following commands to add the IPv4 address, 172.16.23.3, as the DHCP server:

switch(config)# dhcp server
switch(config-dhcp-server)# next-server 172.16.23.3
switch(config-dhcp-server)#

dhcp server option

The dhcp server option command configures DHCP server options. Execute this command in the DHCP Server Configuration Mode.

Command Mode

DHCP Server Configuration

DHCP Server IPv4 or IPv6 Subnet Configuration

Command Syntax

dhcp server option ipv4 code [always-send data type [hex |string] data]] quoted_string hex [client-id disable] hours hours minutes minutes

dhcp server option ipv6 code [always-send data type [hex |string] data]] quoted_string hex [client-id disable] hours hours minutes minutes

Parameters

  • [ipv4|ipv6] - Configure the option for IPv4 or IPv6.
  • code- Specify the option number from the DHCP options.
  • [always-send data type [hex |string] data]] quoted_string hex - Specify to send the option whether or not the client requested it.
  • type hex data hex_number - Specify the option type
  • client-id disable - Prevent the DHCPv4 server from sending back the client ID.

Example

Use the dhcp server option command to add an IPv4 DHCP code, 67, to the DHCP configuration. 
switch(config-dhcp-server)# option ipv4 option 67

dhcp server private-option

The dhcp server private-option command configures DHCP server private options. Execute this command in the DHCP Server Configuration Mode.

Command Mode

DHCP Server Configuration Mode

Command Syntax

dhcp server private-option [ipv4|ipv6] code [always-send data type [hex |string] data]] quoted_string hex

Parameters

  • [ipv4|ipv6] - Configure the option for IPv4 or IPv6.
  • code- Specify the option number from 224 to 254.
  • [always-send data type [hex |string] data]] quoted_string >hex - Specify to send the option whether or not the client requested it.

Example

Use the dhcp server option command to add an IPv4 private option code, 225, to always send the option to the DHCP configuration. 
switch(config-dhcp-server)# option ipv4 private-option 225 always-send private-option ipv4 225 always-send type string data "Code Sent"

dhcp server subnet

The dhcp server subnet command configures DHCP server subnet options. Execute this command in the DHCP Server Configuration Mode.

Command Mode

DHCP Server Configuration Mode

Command Syntax

dhcp server subnet ipv4_address ipv6_address

Parameters

  • ipv4_address - Configure the IPv4 subnet.
  • ipv6_address - Configure the IPv6 subnet.

Example

Use the dhcp server subnet command to add an IPv4 subnet, 198.168.0.0/24, to the DHCP configuration. 
switch(config-dhcp-server)# subnet 198.168.0.0/24

dhcp server subnet client

The dhcp server subnet [ipv4 | ipv6] client command configures client options for the DHCP server. Execute this command in the DHCP Server Configuration Mode.

Command Mode

DHCP Server Configuration Mode

Command Syntax

dhcp server subnet [ipv4|ipv6] client class definition client_class [default-gateway|dns|lease|name|range|reservations|tftp]

Parameters

  • [ipv4|ipv6] - Select the IP address family.
  • definition client_class - Add a class for the client definition.
  • default-gateway ip_address - Configure the client class default gateway sent to DHCP clients.
  • dns server - Configure the client class DNS.
  • lease days hourshours minutesminutes - Configure the client class lease in days, hours, and minutes.
  • name name - Configure the subnet name.
  • range ip_address_start ip_address_end - Configure the range of IP addresses for the subnet.
  • reservations mac-address mac_address [hostname | ipv4-address]- Configure the MAC address to use for reservations.
  • tftp - Configure the client class's TFTP options.

Example

Use the dhcp server subnet ipv4 client class default-gateway command to add a client definition for the IPv4 DHCP client class default gateway of 10.0.0.1. options.
switch(config-dhcp-server)#subnet ipv4 client class ipv4 definition test1 default-gateway 10.0.0.1

dhcp server tftp

The dhcp server tftp command configures DHCP server TFTP options. Execute this command in the DHCP Server Configuration Mode.

Command Mode

DHCP Server Configuration Mode

Command Syntax

dhcp server tftp server [file [ipv4|ipv6] file_name] [option [150|66]] ipv4

Parameters

  • file [ipv4|ipv6] file_name - Configure the IPv4 or IPv6 boot file name.
  • option [150|66]] ipv4 ip_address - Configure the TFTP DHCP option as 150 or 66 with an IPv4 address.

Example

Use the dhcp server tftp command to add option 150 with an IPv4 address 198.168.0.11, to the DHCP configuration. 
switch(config-dhcp-server)# tftp option 150 ipv4 198.168.0.11

dhcp server vendor-option

The dhcp server vendor-option command configures the DHCP server vendor identifier options. Execute this command under the DHCP Server Configuration Mode.

Command Mode

DHCP Server Configuration Mode

Command Syntax

dhcp server vendor-option ipv4 vendor_id default vendor_id sub-option sub-option_code

Parameters

  • vendor_id - Configure the vendor identifier.
  • default vendor_id - Set as the default vendor specific option.
  • sub-option sub-option_code - Set the sub-option code from 1-254.

Example

Use the dhcp server vendor-option command to add vendor option, 1:4:c0:0:2:8 , to the DHCP configuration. 
switch(config-dhcp-server)# vendor-option ipv4 1:4:c0:0:2:8

dhcp server vendor-option ipv4 sub-option

The dhcp server vendor-option command configures the DHCP server vendor identifier options. Execute this command in the DHCP Server Configuration Mode.

Command Mode

DHCP Server Configuration Mode

Command Syntax

dhcp server vendor-option ipv4 vendor_id default vendor_id sub-option sub-option_code type [array | ipv4-address | string] array [ipv4-address data ip_address [string data quoted_string

Parameters

  • vendor_id - Configure the vendor identifier.
  • default vendor_id - Set as the default vendor specific option.
  • sub-option sub-option_code - Set the sub-option code from 1-254.

Example

Use the dhcp server vendor-option command to add the vendor option, 1:4:c0:0:2:8, to the DHCP Server configuration. 
switch(config-dhcp-server)# vendor-option 1:4:c0:0:2:8

ip dhcp relay all-subnets

The ip dhcp relay all-subnets command configures the DHCP smart relay status in the Interface Configuration Mode. DHCP smart relay supports forwarding DHCP requests with a client secondary IP addresses in the gateway address field. Enabling DHCP smart relay on an interface requires that you enable DHCP relay on that interface.

By default, an interface assumes the global DHCP smart relay setting as configured by the ip dhcp relay all-subnets default command. The ip dhcp relay all-subnets command, when configured, takes precedence over the global smart relay setting.

The no ip dhcp relay all-subnets command disables DHCP smart relay on the configuration mode interface. The default ip dhcp relay all-subnets command restores the interface to the default DHCP smart relay setting, as configured by the ip dhcp relay all-subnets default command, by removing the corresponding ip dhcp relay all-subnets or no ip dhcp relay all-subnets statement from running-config.

Command Mode

Interface-Ethernet Configuration

Interface-Port-channel Configuration

Interface-VLAN Configuration

Command Syntax

ip dhcp relay all-subnets

no ip dhcp relay all-subnets

default ip dhcp relay all-subnets

Examples
  • This command enables DHCP smart relay on VLAN interface 100.
    switch(config)# interface vlan 100
switch(config-if-Vl100)# ip helper-address 10.4.4.4
switch(config-if-Vl100)# ip dhcp relay all-subnets
switch(config-if-Vl100)# show ip dhcp relay
DHCP Relay is active
DHCP Relay Option 82 is disabled
DHCP Smart Relay is enabled
Interface: Vlan100
  DHCP Smart Relay is enabled
  DHCP servers: 10.4.4.4
switch(config-if-Vl100)#

  • This command disables DHCP smart relay on VLAN interface 100.
    switch(config-if-Vl100)# no ip dhcp relay all-subnets
switch(config-if-Vl100)# show active
 interface Vlan100
   no ip dhcp relay all-subnets
   ip helper-address 10.4.4.4
switch(config-if-Vl100)# show ip dhcp relay
DHCP Relay is active
DHCP Relay Option 82 is disabled
DHCP Smart Relay is enabled
Interface: Vlan100
  DHCP Smart Relay is disabled
  DHCP servers: 10.4.4.4
switch(config-if-Vl100)#

  • This command enables DHCP smart relay globally, configures VLAN interface 100 to use the global setting, then displays the DHCP relay status.
    switch(config)# ip dhcp relay all-subnets default
switch(config)# interface vlan 100
switch(config-if-Vl100)# ip helper-address 10.4.4.4
switch(config-if-Vl100)# default ip dhcp relay
switch(config-if-Vl100)# show ip dhcp relay
DHCP Relay is active
DHCP Relay Option 82 is disabled
DHCP Smart Relay is enabled
Interface: Vlan100
  Option 82 Circuit ID: 333
  DHCP Smart Relay is enabled
  DHCP servers: 10.4.4.4
switch(config-if-Vl100)#

ip dhcp relay all-subnets default

The ip dhcp relay all-subnets default command configures the global DHCP smart relay setting. DHCP smart relay supports forwarding DHCP requests with a client secondary IP addresses in the gateway address field. The default global DHCP smart relay setting is disabled.

The global DHCP smart relay setting applies to all interfaces for which an ip dhcp relay all-subnets statement does not exist. Enabling DHCP smart relay on an interface requires that you also enable DHCP relay on that interface.

The no ip dhcp relay all-subnets default and default ip dhcp relay all-subnets default commands restore the global DHCP smart relay default setting of disabled by removing the ip dhcp relay all-subnets default command from running-config.

Command Mode

Global Configuration

Command Syntax

ip dhcp relay all-subnets default

no ip dhcp relay all-subnets default

default ip dhcp relay all-subnets default

Example

This command configures the global DHCP smart relay setting to enabled.
switch(config)# ip dhcp relay all-subnets default
switch(config)#

ip dhcp relay always-on

The ip dhcp relay always-on command enables the DHCP relay agent on the switch regardless of the DHCP relay agent status on any interface. By default, EOS enables the DHCP relay agent only if you have one routable interface configured with an ip helper-address statement.

The no ip dhcp relay always-on and default ip dhcp relay always-on commands remove the ip dhcp relay always-on command from running-config.

Command Mode

Global Configuration

Command Syntax

ip dhcp relay always-on

no ip dhcp relay always-on

default ip dhcp relay always-on

Example

This command enables the DHCP relay agent.
switch(config)# ip dhcp relay always-on
switch(config)#

ip dhcp relay information option (Global)

The ip dhcp relay information option command configures the switch to attach tags to DHCP requests before forwarding them to the DHCP servers designated by the ip helper-address commands. The command specifies the tag contents for packets forwarded by the configured interface. The default value for each interface configured with an ip helper-address is the name and number of the interface.

The no ip dhcp relay information option and default ip dhcp relay information option commands restore the switch default setting of not attaching tags to DHCP requests by removing the ip dhcp relay information option command from running-config.

Command Mode

DHCP Relay Configuration

Command Syntax

ip dhcp relay information option [circuit-id | remote-id] encoding [%p | %x]] [vendor-option]

no ip dhcp relay information option

default ip dhcp relay information option

Example

This command enables the attachment of tags to DHCP requests forwarded to DHCP server addresses with the circuit ID as a string:
switch(config)# ip dhcp relay information option
switch(config-information-option)# circuit-id encoding %p

ip dhcp relay information option circuit-id

The ip dhcp relay information option circuit-id command specifies the content of tags that the switch attaches to DHCP requests before forwarding them from the configuration mode interface to DHCP server addresses specified by ip helper-address commands. Tags attach to outbound DHCP requests only if you enable the information option on the switch (ip dhcp relay information option circuit-id).

The no ip dhcp relay information option circuit-id and default ip dhcp relay information option circuit-id commands restore the default content setting for the configuration mode interface by removing the corresponding command from running-config.

Command Mode

Interface-Ethernet Configuration

Interface-Loopback Configuration

Interface-Management Configuration

Interface-Port-channel Configuration

Interface-VLAN Configuration

Command Syntax

ip dhcp relay information option circuit-id id_label

no ip dhcp relay information option circuit-id

default ip dhcp relay information option circuit-id

Parameters

id_label- Specifies the tag content. Use a format in alphanumeric characters (maximum 15 characters).

Example

This command configures x-1234 as the tag content for packets send from VLAN 200. 
switch(config)# interface vlan 200
switch(config-if-Vl200)# ip dhcp relay information option circuit-id x-1234
switch(config-if-Vl200)#

ip dhcp snooping

The ip dhcp snooping command enables DHCP snooping globally on the switch. Configure DHCP snooping as a set of Layer 2 processes and use it with DHCP servers to control network access to clients with specific IP/MAC addresses. The switch supports Option-82 insertion,a DHCP snooping process that allows relay agents to provide remote-ID and circuit-ID information to DHCP reply and request packets. DHCP servers use this information to determine the originating port of DHCP requests and associate a corresponding IP address to that port. DHCP servers use port information to track host location and IP address usage by authorized physical ports.

DHCP snooping uses the information option (Option-82) to include the switch MAC address as the router-ID along with the physical interface name and VLAN number as the circuit-ID in DHCP packets. After adding the information to the packet, the DHCP relay agent forwards the packet to the DHCP server as specified by the DHCP protocol.

DHCP snooping on a specified VLAN requires all of these conditions to be met:
  • Enable DHCP snooping globally.
  • Enabled insertion of option-82 information in DHCP packets.
  • Enable DHCP snooping on the specified VLAN.
  • Enable DHCP relay on the corresponding VLAN interface.

The no ip dhcp snooping and default ip dhcp snooping commands disables global DHCP snooping by removing the ip dhcp snooping command from running-config.

Command Mode

Global Configuration

Command Syntax

ip dhcp snooping

no ip dhcp snooping

default ip dhcp snooping

Related Commands

Example

This command globally enables snooping on the switch, displaying DHCP snooping status prior and after invoking the command.
switch(config)# show ip dhcp snooping
DHCP Snooping is disabled
switch(config)# ip dhcp snooping
switch(config)# show ip dhcp snooping
DHCP Snooping is enabled
DHCP Snooping is not operational
DHCP Snooping is configured on following VLANs:
  None
DHCP Snooping is operational on following VLANs:
  None
Insertion of Option-82 is disabled
switch(config)#

ip dhcp snooping bridging

The ip dhcp snooping bridging command enables the DHCP snooping bridging configuration.

The no ip dhcp snooping bridging command removes the DHCP snooping bridging configuration from the running-config.

Command Mode

Global Configuration Mode

Command Syntax

ip dhcp snooping bridging

no ip dhcp snooping bridging

Example

This command configures the DHCP snooping bridging. 
switch# configure
switch(config)# ip dhcp snooping bridging

ip dhcp snooping information option

The ip dhcp snooping information option command enables the insertion of option-82 DHCP snooping information in DHCP packets on VLANs where you have DHCP snooping enabled. DHCP snooping provides a Layer 2 switch process that allows relay agents to provide remote-ID and circuit-ID information to DHCP reply and request packets. DHCP servers use this information to determine the originating port of DHCP requests and associate a corresponding IP address to that port.

DHCP snooping uses information option (Option-82) to include the switch MAC address (router-ID) along with the physical interface name and VLAN number (circuit-ID) in DHCP packets. After adding the information to the packet, the DHCP relay agent forwards the packet to the DHCP server through DHCP protocol processes.

DHCP snooping on a specified VLAN requires all of these conditions to be met:
  • Enable DHCP snooping globally.
  • Enabled insertion of option-82 information in DHCP packets.
  • Enable DHCP snooping on the specified VLAN.
  • Enable DHCP relay on the corresponding VLAN interface.

Ifnot enabling DHCP snooping globally, the ip dhcp snooping information option command persists in running-config without any operational effect.

The no ip dhcp snooping information option and default ip dhcp snooping information option commands disable the insertion of option-82 DHCP snooping information in DHCP packets by removing the ip dhcp snooping information option statement from running-config.

Command Mode

Global Configuration

Command Syntax

ip dhcp snooping information option

no ip dhcp snooping information option

default ip dhcp snooping information option

Example

These commands enable DHCP snooping on DHCP packets from ports on snooping-enabled VLANs. DHCP snooping was previously enabled on the switch.
switch(config)# ip dhcp snooping information option
switch(config)# show ip dhcp snooping
DHCP Snooping is enabled
DHCP Snooping is operational
DHCP Snooping is configured on following VLANs:
  100
DHCP Snooping is operational on following VLANs:
  100
Insertion of Option-82 is enabled
  Circuit-id format: Interface name:Vlan ID
  Remote-id: 00:1c:73:1f:b4:38 (Switch MAC)
switch(config)#

ip dhcp snooping vlan

The ip dhcp snooping vlan command enables DHCP snooping on specified VLANs. DHCP snooping provides a Layer 2 process that allows relay agents to provide remote-ID and circuit-ID information in DHCP packets. DHCP servers use this data to determine the originating port of DHCP requests and associate a corresponding IP address to that port. Configure DHCP snooping on a global and VLAN basis.

VLAN snooping on a specified VLAN requires each of these conditions:
  • Enable DHCP snooping globally.
  • Enable insertion of option-82 information in DHCP packets.
  • Enable DHCP snooping on the specified VLAN.
  • Enable DHCP relay on the corresponding VLAN interface.

If not enabling global DHCP snooping, the ip dhcp snooping vlan command persists in running-config without any operational affect.

The no ip dhcp snooping information option and default ip dhcp snooping information option commands disable DHCP snooping operability by removing the ip dhcp snooping information option statement from running-config.

Command Mode

Global Configuration

Command Syntax

ip dhcp snooping vlan v_range

no ip dhcp snooping vlan v_range

default ip dhcp snooping vlan v_range

Parameters
  • v_range - Specifies the range of VLANs to enable DHCP snooping. Formats include a number, a number range, or a comma-delimited list of numbers and ranges. Numbers range from 1 to 4094.

Example

These commands enable DHCP snooping globally, DHCP snooping on VLAN interface 100, and DHCP snooping on vlan100.
switch(config)# ip dhcp snooping
switch(config)# ip dhcp snooping information option
switch(config)# ip dhcp snooping vlan 100
switch(config)# interface vlan 100
switch(config-if-Vl100)# ip helper-address 10.4.4.4
switch(config-if-Vl100)# show ip dhcp snooping
DHCP Snooping is enabled
DHCP Snooping is operational
DHCP Snooping is configured on following VLANs:
  100
DHCP Snooping is operational on following VLANs:
  100
Insertion of Option-82 is enabled
  Circuit-id format: Interface name:Vlan ID
  Remote-id: 00:1c:73:1f:b4:38 (Switch MAC)
switch(config)#

ipv6 dhcp relay always-on

The iv6p dhcp relay always-on command enables the switch DHCP relay agent on the switch regardless of the DHCP relay agent status on any interface. By default, the DHCP relay agent is enabled only if at least one routable interface is configured with an ipv6 dhcp relay destination statement.

The no ipv6 dhcp relay always-on and default ipv6 dhcp relay always-on commands remove the ipv6 dhcp relay always-on command from running-config.

Command Mode

Global Configuration

Command Syntax

ipv6 dhcp relay always-on

no ipv6 dhcp relay always-on

default ipv6 dhcp relay always-on

Example
This command enables the DHCP relay agent.
switch(config)# ipv6 dhcp relay always-on
switch(config)#

ipv6 dhcp relay destination

The ipv6 dhcp relay destination command enables the DHCPv6 relay agent and sets the destination address on the configuration mode interface.

The no ipv6 dhcp relay destination and default ipv6 dhcp relay destination commands remove the corresponding ipv6 dhcp relay destination command from running-config. When the commands do not list an IPv6 address, all ipv6 dhcp relay destination commands are removed from running-config.

Command Mode

Interface-Ethernet Configuration

Interface-Port-channel Configuration

Interface-VLAN Configuration

Command Syntax

ipv6 dhcp relay destination [ipv6_addr][source-address ipv6_addr]

no ipv6 dhcp relay destination [ipv6_addr]

default ipv6 dhcp relay destination [ipv6_addr]

Parameters
  • ipv6_addr     DCHP Server’s IPv6 address.
  • source-address ipv6_addr specify the source IPv6 address to communicate with DHCP server.

Guidelines

If the source-address parameter is specified, then the DHCP client receives an IPv6 address from the subnet of source IP address. The source-address must be one of the configured addresses on the interface.

Example

This command enables the DHCPv6 relay agent and sets the destination address to 2001:0db8:0:1::1 on interface ethernet 4.

switch(config)# interface ethernet 4
switch(config-if-Et4)# ipv6 dhcp relay destination 2001:0db8:0:1::1
switch(config-if-Et4)# show ip dhcp relay
DHCP Relay is active
DHCP Relay Option 82 is disabled
DHCPv6 Relay Link-layer Address Option (79) is disabled
DHCP Smart Relay is disabled
Interface: Ethernet4
  DHCP Smart Relay is disabled
  DHCP servers: 1::1
                2001:db8:0:1::1
switch(config-if-Et4)#

ipv6 dhcp relay option link-layer address

The ipv6 dhcp relay option link-layer address command enables the DHCPv6 relay agent to configure the client link layer address option to solicit and request messages. In other words, the command enables the link layer address option (79) in the global configuration mode.

The no ipv6 dhcp relay option link-layer address command disables the link layer address option (79) in the global configuration mode.

Command Mode

Global Configuration

Command Syntax

ipv6 dhcp relay option link-layer address

no ipv6 dhcp relay option link-layer address

default ipv6 dhcp relay option link-layer address

Example

This command enables the insertion of link layer address option (79) in the global configuration mode.
switch(config)# ipv6 dhcp relay option link-layer address

ipv6 dhcp relay option remote-id

The ipv6 dhcp relay option command configures DHCPv6 Relay Option 37, Remote-ID, to add the MAC address, interface ID or name, and hostname as the remote-id format. The no version of the command removes the configuration from the running-config.

Command Mode

Global Configuration

Command Syntax

ipv6 dhcp relay option remote-id format {%m:%h:%p | %m:%i | %m:%p}

no ipv6 dhcp relay option remote-id format {%m:%h:%p | %m:%i | %m:%p}

Parameters

  • remote-id - Add Option 37 to the DHCP Relay configuration.
  • format - Select one of the following as the format for the remote-id:
    • %m:%h:%p - Specify the MAC address, hostname, and interface name as the remote-id.
    • %m:%i - Specify the MAC address and interface ID as the remote-id.
    • %m:%p - Specify the MAC address and interface name as the remote-id.

Example

Use the following command to specify using the MAC address, hostname, and interface name for the Remote-ID:

switch(config)# ipv6 dhcp relay option remote-id format %m:%h:%p

ipv6 dhcp snooping

The ipv6 dhcp snooping command enables DHCP snooping globally on the switch.

The no ipv6 dhcp snooping and default ipv6 dhcp snooping commands disable global DHCP snooping by removing the ipv6 dhcp snooping command from running-config.

Command Mode

Global Configuration

Command Syntax

ipv6 dhcp snooping [remote-id option | vlan [$ | vlan-range]]

no ipv6 dhcp snooping [remote-id option | vlan [$ | vlan-range]]

default ipv6 dhcp snooping [remote-id option | vlan [$ | vlan-range]]

Parameters
  • remote-id option configures the remote ID option.
  • vlan enables IPv6 DHCP snooping for a specific VLAN. Numbers range from 1 to 4094.
  • $ end of range.
  • vlan-range VLANs based on the snooping enabled. Formats include a number, a number range, or a comma-delimited list of numbers and ranges. Numbers range from 1 to 4094.

Examples

  • The following configuration enables IPv6 DHCP snooping feature at the global level.

    switch(config)# ipv6 dhcp snooping
switch(config)# ipv6 dhcp snooping remote-id option
switch(config)# ipv6 dhcp snooping vlan <vlan|vlan-range>

  • The following command display IPv6 DHCP snooping state.
    switch(config)# ipv6 dhcp snooping
switch(config)# show ipv6 dhcp snooping
DHCPv6 Snooping is enabled
DHCPv6 Snooping is operational
DHCPv6 Snooping is configured on following VLANs:
  2789-2790
DHCPv6 Snooping is operational on following VLANs:
  2789
Insertion of Option-37 is enabled

name

The name command in DHCP Server Subnet Configuration Mode creates a name for the subnet and improves readability of the subnet list.

The [no | default] versions of the command disable the feature and remove the configuration from the running-config.

Command Mode

DHCP Server IPv4 or IPv6 Subnet Configuration

Command Syntax

name

no name

default name

Parameters

  • name name - Specify a name for the subnet.

Example

Use the following commands to configure a name, remote_switch, to subnet 172.16.23.11/32:

switch(config)# dhcp server
switch(config-dhcp-server)# subnet 172.16.23.11/32
switchconfig-dhcp-subnet-ipv4)# name remote_switch
switchconfig-dhcp-subnet-ipv4)#

prefix-delegation

The prefix-delegation command in DHCP Server IPv6 Subnet Configuration Mode configures a block of IPv6 addresses for a downstream router on the network. The router then splits the block into subnets and assigns the IPv6 addresses to devices on its network.

The [no | default] versions of the command disable the feature and remove the configuration from the running-config.

Command Mode

DHCP Server IPv6 Subnet Configuration

Command Syntax

prefix-delegation

no prefix-delegation

default prefix-delegation

Parameters

  • prefix-delegation ipv6_address_range - Specify a block of IPv6 addresses for the IPv6 subnet.

Example

Use the following commands to delegate a block of IPv6 addresses, 2001:db8:100:aa00::/56, to subnet 2001:db8:100::/48:

switch(config)# dhcp server
switch(config-dhcp-server)# subnet 2001:db8:100::/48
switchconfig-dhcp-subnet-ipv6)# prefix-delegation 2001:db8:100:aa00::/56
switchconfig-dhcp-subnet-ipv6)#

range

The range command in DHCP Server Subnet Configuration Mode explicitly defines the contiguous block of IP addresses that the DHCP server is allowed to dynamically lease to clients.

The [no | default] versions of the command disable the feature and remove the configuration from the running-config.

Command Mode

DHCP Server IPv6 Subnet Configuration

Command Syntax

subnet [ipv4 | ipv6] range start_ipaddress end_ipaddress

no range

default range

Parameters

  • subnet [ipv4 \ ipv6] - Specify an IPv4 or IPv6 address for the subnet.
  • range start_ipaddress end_ipaddress - Specify a range for the subnet.

Example

Use the following commands to configure a name, remote_switch, to subnet 172.16.23.11/32:

switch(config)# dhcp server
switch(config-dhcp-server)# subnet 172.16.23.11/32
switchconfig-dhcp-subnet-ipv4)# range 172.16.23.100 172.16.23.200
switchconfig-dhcp-subnet-ipv4)#

reservations mac-address

The reservations mac-address command in DHCP Server IPv4 Subnet Reservations Configuration Mode builds static DHCP bindings from the client MAC address on the reservations list. Once in the DHCP Server IPv4 Subnet Reservations MAC Address Configuration Mode, add reservations for a hostname and an IPv4 address to map to the MAC address.

The [no | default] versions of the command disable the feature and remove the configuration from the running-config.

Command Mode

DHCP Server IPv4 Subnet Reservations Configuration

Command Syntax

reservations mac-address

Parameters

  • reservations mac-address mac_address - Specify a MAC address reservation for the subnet.
  • hostname hostname - Specify a host name to map to the MAC address.
  • ipv4-address ip_address - Specify an IPv4 address to map to the MAC address.

Example

Use the following commands to configure a reservation for MAC address, 80:A9:97:27:1A:AC, and IPv4 address, 172.26.23.25 to the subnet reservation. 172.16.23.11/32:

switch(config)# dhcp server
switch(config-dhcp-server)# subnet 172.16.23.11/32
switchconfig-dhcp-subnet-ipv4)# reservations
switchconfig-dhcp-subnet-ipv4-reserve)# mac-address 80:A9:97:27:1A:AC
switchconfig-dhcp-subnet-ipv4-rsrv-mac-address)# ipv4-address 172.26.23.25
switchconfig-dhcp-subnet-ipv4-rsrv-mac-address)#

show dhcp server

Use the show dhcp server command to display DHCP server information.

Command Mode

EXEC

Command Syntax

show dhcp server [ipv4 | ipv6 | leases | vrf]

Parameters
  • ipv4 Displays details related to IPv4.
  • ipv6 Displays details related to IPv6.
  • leases Displays active leases.
    • A.B.C.D/E IPv4 subnet.
    • NAME Subnet name.
Examples

  • The following output displays DHCPv4.

    switch# show dhcp server ipv4
IPv4 DHCP Server is active
Debug log is enabled
DNS server(s): 10.2.2.2
DNS domain name: mydomain
Lease duration: 1 days 0 hours 0 minutes
TFTP server:
myserver (Option 66)
10.0.0.3 (Option 150)
TFTP file: fileFoo
Active Leases: 1
IPv4 DHCP interface status:
   Interface   Status
-------------------------------------------------
   Ethernet1   Inactive (Could not determine VRF)
   Ethernet2   Inactive (Not in default VRF)
   Ethernet3   Inactive (Kernel interface not created yet)
   Ethernet4   Inactive (Not up)
   Ethernet5   Inactive (No IP address)
   Ethernet6   Active

Vendor information:
Vendor ID: default
  Sub-options         Data       
---------------- ----------------
      1          192.0.2.0, 192.0.2.1

Vendor ID: vendorFoo
  Sub-options       Data       
---------------- -----------
      2            192.0.2.2
      3            “data”

Subnet: 10.0.0.0/8
Subnet name: subnetFoo
Range: 10.0.0.1 to 10.0.0.10
DNS server(s): 10.1.1.1 10.2.2.2
Lease duration: 3 days 3 hours 3 minutes
Default gateway address: 10.0.0.3
TFTP server:
subnetServerFoo (Option 66)
10.0.0.4 (Option 150)
TFTP boot file: subnetFiletftp
Active leases: 1
Reservations:
MAC address: 1a1b.1c1d.1e1f
IPv4 address: 10.0.0.1

MAC address: 2a2b.2c2d.2e2f    
IPv4 address: 10.0.0.2

  • In this example, DHCPv6 is configured with subnet fe80::/10 while being enabled on Ethernet1 with address fe80::1/64 and on Ethernet3 with address fe80::2/64.
    switch# show dhcp server ipv6
IPv6 DHCP server is active
Debug log is enabled                                                                                                                                                                                                                     
DNS server(s): fe80::6                                                                                                                                                                                                                     
DNS domain name: testaristanetworks.com                                                                                                                                                                                                        
Lease duration: 1 days 3 hours 30 minutes                                                                                                                                                                                                      
Active leases: 0                                                                                                                                                                                                                               
IPv6 DHCP interface status:                                                                                                                                                                                                                    
   Interface    Status                                                                                                                                                                                                                         
--------------- ------                                                                                                                                                                                                                         
   Ethernet1    Active
   Ethernet3    Active                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                               
Subnet: fe80::/10                                                                                                                                                                                                                      
Subnet name: foo                                                                                                                                                                                                                                                                                                                                                                                                                                     
Range: fe80::1 to fe80::3
DNS server(s): fe80::4 fe80::5                                                                                                                                                                                                                                                                                                                                                                                                                                          
Direct: Inactive (Multiple interfaces match this subnet: Ethernet1 Ethernet3)
Relay: Active                                                                                                                                                                                                                            
Active leases: 0

  • This example illustrates when multiple subnets match an interface. In this example, DHCPv6 is configured with subnets fc00::/7 and fe80::/10 while being enabled on Ethernet1 with address fe80::1/10 and fc00::1/7.
    switch# show dhcp server ipv6
IPv6 DHCP server is active                                                                                                                                                                                                                     
DNS server(s):  fc00::2                                                                                                                                                                                                                     
DNS domain name: testaristanetworks.com                                                                                                                                                                                                        
Lease duration: 1 days 3 hours 30 minutes                                                                                                                                                                                                      
Active leases: 0                                                                                                                                                                                                                               
IPv6 DHCP interface status:                                                                                                                                                                                                                    
   Interface    Status                                                                                                                                                                                                                         
--------------- ------                                                                                                                                                                                                                         
   Ethernet1    Active                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                               
Subnet: fc00::/7                                                                                                                                                                                                                      
Subnet name: data                                                                                                                                                                                                                               
Range: fc00::1 to fc00::5                                                                                                                                                                                                       
DNS server(s): fc00::6 fc00::8                                                                                                                                                                                                                                                                                                                                                                                                                                          
Direct: Inactive (This and other subnets match interface Ethernet1)
Relay: Active
                                                                                                                                                                                                                                  
Active leases: 0

Subnet: fe80::/10                                                                                                                                                                                                                      
Subnet name: bar                                                                                                                                                                                                                                                                                                                                                                                                                                         
Direct: Inactive (This and other subnets match interface Ethernet1)
Relay: Active
                                                                                                                                                                                                                                  
Active leases: 0

  • After disabling a subnet, the show dhcp server command displays the disable message with a reason. The number of active leases of the disabled subnets displays as 0. In this example, there are overlapping subnets.
    switch# show dhcp server
IPv4 DHCP Server is active
DNS server(s): 10.2.2.2
Lease duration: 1 days 0 hours 0 minutes
Active Leases: 0
IPv4 DHCP interface status:
   Interface   Status
-------------------------------------------------
   Ethernet1   Active

Subnet: 10.0.0.0/24 (Subnet is disabled - overlapping subnet 10.0.0.0/8)
Range: 10.0.0.1 to 10.0.0.10
DNS server(s): 10.3.3.3 10.4.4.4
Default gateway address: 10.0.0.4
Active leases: 0

Subnet: 10.0.0.0/8 (Subnet is disabled - overlapping subnet 10.0.0.0/24)
DNS server(s):
Default gateway address: 10.0.0.3
Active leases: 0

  • In this example, the display output shows overlapping ranges.
    switch# show dhcp server
IPv4 DHCP Server is active
DNS server(s): 10.2.2.2
Lease duration: 1 days 0 hours 0 minutes
Active Leases: 0
IPv4 DHCP interface status:
   Interface   Status
-------------------------------------------------
   Ethernet1   Active

Subnet: 10.0.0.0/8 (Subnet is disabled - range 10.0.0.9-10.0.0.12 overlaps with an existing pool)
Range: 10.0.0.1 to 10.0.0.10
Range: 10.0.0.9 to 10.0.0.12
DNS server(s): 10.3.3.3 10.4.4.4
Default gateway address: 10.0.0.4
Active leases: 0

  • This example displays duplicate static IP address reservation.
    Subnet: 10.0.0.0/8 (Subnet is disabled - ipv4-address 10.0.0.11 is reserved more than once)
Subnet name:
DNS server(s):
Default gateway address: 10.0.0.3
Active leases: 0
Reservations:
MAC address: 1a1b.1c1d.1e1f    
IPv4 address: 10.0.0.11

MAC address: 2a2b.2c2d.2e2f    
IPv4 address: 10.0.0.11

  • Use the show dhcp server leases command to display detailed information about the IP addresses allocated by the DHCP Server (including the IP address, the expected end time for that address, the time when the address is handed out, and the equivalent MAC address).
    switch# show dhcp server leases
10.0.0.10
End: 2019/06/20 17:44:34 UTC
Last transaction: 2019/06/19 17:44:34 UTC
MAC address: 5692.4c67.460a

2000:0:0:40::b                                                                                                                                                                                                                                 
End: 2019/06/20 18:06:33 UTC                                                                                                                                                                                                                   
Last transaction: 2019/06/20 14:36:33 UTC                                                                                                                                                                                                      
MAC address: 165a.a86d.ffac

show dhcp server leases

Use the show dhcp server leases command to display DHCP server lease information.

Command Mode

EXEC

Command Syntax

show dhcp server leases [ipv4 | ipv6]

Parameters
  • ipv4 - Displays details related to IPv4.
  • ipv6 - Displays details related to IPv6.

Example

Use the show dhcp server leases command to display detailed information about the IP addresses allocated by the DHCP Server including the IP address, the expected end time for that address, the time when assigning the address, and the equivalent MAC address.
switch# show dhcp server leases
10.0.0.10
End: 2019/06/20 17:44:34 UTC
Last transaction: 2019/06/19 17:44:34 UTC
MAC address: 5692.4c67.460a

2000:0:0:40::b                                                                                                                                                                                                                                 
End: 2019/06/20 18:06:33 UTC                                                                                                                                                                                                                   
Last transaction: 2019/06/20 14:36:33 UTC                                                                                                                                                                                                      
MAC address: 165a.a86d.ffac

show ip dhcp relay

The show ip dhcp relay command displays the DHCP relay agent configuration status on the switch.

Command Mode

EXEC

Command Syntax

show ip dhcp relay

Example

This command displays the DHCP relay agent configuration status.
switch> show ip dhcp relay
DHCP Relay is active
DHCP Relay Option (82)is enabled
DHCP Relay vendor-specific suboption (9) under information option (82)
DHCP Smart Relay is enabled
Interface: Vlan100
  DHCP Smart Relay is disabled
  DHCP servers: 10.4.4.4
switch>

show ip dhcp relay counters

The show ip dhcp relay counters command displays the number of DHCP packets received, forwarded, or dropped on the switch and on all interfaces enabled as DHCP relay agents.

Command Mode

EXEC

Command Syntax

show ip dhcp relay counters

Example

This command displays the IP DHCP relay counter table.
switch> show ip dhcp relay counters

          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop |         Last Cleared
----------|----- ---- -----|---------------------
  All Req |  376  376    0 | 4 days, 19:55:12 ago
 All Resp |  277  277    0 |
          |                |
 Vlan1000 |    0    0    0 | 4 days, 19:54:24 ago
 Vlan1036 |  376  277    0 | 4 days, 19:54:24 ago

switch>

show ip dhcp snooping

The show ip dhcp snooping command displays the DHCP snooping configuration.

Command Mode

EXEC

Command Syntax

show ip dhcp snooping

Example

This command displays the switch’s DHCP snooping configuration.
switch> show ip dhcp snooping
DHCP Snooping is enabled
DHCP Snooping is operational
DHCP Snooping is configured on following VLANs:
  100
DHCP Snooping is operational on following VLANs:
  100
Insertion of Option-82 is enabled
  Circuit-id format: Interface name:Vlan ID
  Remote-id: 00:1c:73:1f:b4:38 (Switch MAC)
switch>

show ip dhcp snooping counters

The show ip dhcp snooping counters command displays counters that track the quantity of DHCP request and reply packets received by the switch. The output displays data for each VLAN or aggregated for all VLANs with counters for packets dropped.

Command Mode

EXEC

Command Syntax

show ip dhcp snooping counters [counter_typedebug]

Parameters

counter_type - Displays the type of counter.
  • no parameter - Command displays counters for each VLAN.
  • debug - Command displays aggregate counters and drop cause counters.

Examples
  • This command displays the number of DHCP packets sent and received on each VLAN.
    switch> show ip dhcp snooping counters

     | Dhcp Request Pkts | Dhcp Reply Pkts |
Vlan |  Rcvd  Fwdd  Drop | Rcvd Fwdd  Drop | Last Cleared
-----|------ ----- ------|----- ---- ------|-------------
 100 |     0     0     0 |    0    0     0 |  0:35:39 ago

switch>

  • This command displays the number of DHCP packets sent on the switch.
    switch> show ip dhcp snooping counters debug
Counter                       Snooping to Relay Relay to Snooping
----------------------------- ----------------- -----------------
Received                                      0                 0
Forwarded                                     0                 0
Dropped - Invalid VlanId                      0                 0
Dropped - Parse error                         0                 0
Dropped - Invalid Dhcp Optype                 0                 0
Dropped - Invalid Info Option                 0                 0
Dropped - Snooping disabled                   0                 0

Last Cleared:  3:37:18 ago
switch>

show ip dhcp snooping hardware

The show ip dhcp snooping hardware command displays internal hardware DHCP snooping status on the switch.

Command Mode

EXEC

Command Syntax

show ip dhcp snooping hardware

Example

This command DHCP snooping hardware status.
switch> show ip dhcp snooping hardware
DHCP Snooping is enabled
DHCP Snooping is enabled on following VLANs:
    None
    Vlans enabled per Slice
        Slice:  FixedSystem
        None
switch>

show ipv6 dhcp relay counters

The show ipv6 dhcp relay counters command displays the number of DHCP packets received, forwarded, or dropped on the switch and on all interfaces enabled as DHCP relay agents.

Command Mode

EXEC

Command Syntax

show ipv6 dhcp relay counters

Example

This command displays the IP DHCP relay counter table.
switch> show ipv6 dhcp relay counters
          |  Dhcp Packets  |
Interface | Rcvd Fwdd Drop |         Last Cleared
----------|----- ---- -----|---------------------
  All Req |  376  376    0 | 4 days, 19:55:12 ago
 All Resp |  277  277    0 |
          |                |
Ethernet4 |  207  148    0 | 4 days, 19:54:24 ago

switch>

show ipv6 dhcp snooping

The show ipv6 dhcp snooping command displays information about the DHCP snooping configuration.

Command Mode

EXEC

Command Syntax

show ipv6 dhcp snooping

Related Commands

Example

This command displays the switch’s DHCP snooping configuration.

switch# show ipv6 dhcp snooping
DHCPv6 Snooping is enabled
DHCPv6 Snooping is operational
DHCPv6 Snooping is configured on following VLANs:
  2789-2790
DHCPv6 Snooping is operational on following VLANs:
  2789
Insertion of Option-37 is enabled

show ipv6 dhcp snooping counters

The show ipv6 dhcp snooping counters command displays counters that track the quantity of DHCP request and reply packets that the switch receives. Data is either presented for each VLAN or aggregated for all VLANs with counters for packets dropped.

Command Mode

EXEC

Command Syntax

show ipv6 dhcp snooping counters [COUNTER_TYPE]

Parameters
  • COUNTER_TYPE     The type of counter that the command displays.
  • no parameter     command displays counters for each VLAN.
  • debug     command displays aggregate counters and drop cause counters.

Examples
  • This command displays the number of DHCP packets sent and received on each VLAN.
    switch# show ipv6 dhcp snooping counters

     | Dhcpv6 Request Pkts | Dhcpv6 Reply Pkts | 
Vlan |  Rcvd   Fwdd   Drop |  Rcvd  Fwdd  Drop | Last Cleared
-----|------ ------ -------|------ ----- ------|------------- 
2789 |     1      1      0 |     1     1     0 |  0:03:09 ago

  • This command displays the number of DHCP packets sent on the switch.
    switch# show ipv6 dhcp snooping counters debug

Counter                       Snooping to Relay Relay to Snooping
----------------------------- ----------------- -----------------
Received                                      1                 1
Forwarded                                     1                 1
Dropped - Invalid VlanId                      0                 0
Dropped - Parse error                         0                 0
Dropped - Invalid Dhcp Optype                 0                 0
Dropped - Invalid Remote-ID Option            0                 0
Dropped - Snooping disabled                   0                 0

Last Cleared:  0:04:29 ago

show ipv6 dhcp snooping hardware

The show ipv6 dhcp snooping hardware command displays internal hardware DHCP snooping status on the switch.

Command Mode

EXEC

Command Syntax

show ipv6 dhcp snooping hardware

Example

This command displays DHCP snooping hardware status.

switch# show ipv6 dhcp snooping hardware
DHCPv6 Snooping is enabled
DHCPv6 Snooping is enabled on following VLANs:
    2789
    Vlans enabled per Slice
        Slice:  Linecard0-0
        2789
        Slice:  Linecard0-1
        2789
        Slice:  Linecard0-2
        2789
        Slice:  Linecard0-3
        2789