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Enterprise WAN Router Configuration Guide - ECMP Print

ECMP

Equal-cost multi-path routing (ECMP) is a routing plan where next-hop packet forwarding to a single destination takes place over multiple "best paths" that tie for top place in routing metric calculations. Use multi-path routing with most routing protocols because it is a per-hop decision limited to a single router.

Adding ECMP

Describes how to add ECMP to new or existing VMs.

  1. Have the following line in a device's running configuration.

    If an instance is created with an older, pre-AWE-7200R and CloudEOS router 4.20.5 image, add the command line in the example below.

    Suppose an instance is created with AWE-7200R and CloudEOS router 4.20.5 or later image. In that case, there is no need for additional configuration changes because the command line appears in the configuration by default.

    agent KernelFib environment KERNELFIB_PROGRAM_ALL_ECMP='true'
  2. Reload the device or restart the KernelFib agent via agent KernelFib terminate.
    This step is needed only if the instance was created with an older, pre-AWE-7200R and CloudEOS router 4.20.5 image.
  3. To enable ECMP in a routing protocol, issue the maximum-paths <#> command inside the routing protocol used. 
    AWE-7200R and CloudEOS router# configure terminal
AWE-7200R and CloudEOS router(config)# router bgp 65112
AWE-7200R and CloudEOS router(config-router-bgp)# maximum-paths 16

     

  4. When ECMP starts and there are multiple routes, the display output may be similar to the following example. 
    AWE-7200R and CloudEOS router# show ip route 10.4.3.0

VRF: default
Codes: C - connected, S - static, K - kernel,
 O - OSPF, IA - OSPF inter area, E1 - OSPF external type 1,
 E2 - OSPF external type 2, N1 - OSPF NSSA external type 1,
 N2 - OSPF NSSA external type2, B I - iBGP, B E - eBGP,
 R - RIP, I L1 - IS-IS level 1, I L2 - IS-IS level 2,
 O3 - OSPFv3, A B - BGP Aggregate, A O - OSPF Summary,
 NG - Nexthop Group Static Route, V - VXLAN Control Service,
 DH - DHCP client installed default route, M - Martian

 S10.4.3.0/24 [1/0] via 190.19.11.2, Tunnel1
via 190.19.11.102, Tunnel3

     

  5. To determine the route the interface traffic takes to specific addresses, issue the bash ip route get <address> command to determine which link the traffic uses. In the following example, traffic to 10.4.3.5 takes Tunnel1, while traffic to 10.4.3.6 takes Tunnel3. 
    AWE-7200R and CloudEOS router# bash ip route get 10.4.3.5
10.4.3.5 via 190.19.11.2 dev tun1 src 190.19.11.1
cache
AWE-7200R and CloudEOS router# bash ip route get 10.4.3.6
10.4.3.6 via 190.19.11.102 dev tun3 src 190.19.11.101
cache

     

    For additional information regarding ECMP, refer to the current release notes.
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