Defining Paths

A “path” represents a pair of interfaces (or their IP addresses), a source interface and a destination interface through which traffic can flow from site to site.

For example, in the above figure there are two paths from Router1 to Router2

  1. MPLS path - --
  2. 4 Internet paths
  • --
  • --
  • --
  • --

However, some of the paths are crossing ISPs, for example, -- is going from router1 through ISP1, ISP2 to router2. In some customer scenarios ISP2 could be an LTE SP and could be purely as a backup in case ISP1 fails. In this case the paths -- and -- should not be used.

Path-group similar to nexthop-group is used to group the paths in order to

  • Restrict paths - define which paths are valid among the available paths like the LTE backup SP discussed before
  • Apply specific policies to path group. Eg apply encryption for all Internet paths

Path group commands are configured under “router path-selection” as shown below. The commands are explained in the subsections.

router path-selection
path-group <group-name> 
local interface <intf-name> 
## more local interface commands 
## that belong to the same path-group, eg Internet
peer static router-ip <ip-address> 
ipv4 address <ip-addr1> 
## more IP addresses through which the router can be reached

The router-IP is the same as the VTEP-IP. local is used to configure the local WAN IP address or interface part of the path-group. Peer is used to configure the remote VTEP reachability statically.

Each combination of peer and local IP address is a potential path. If routing resolves the remote IP through a local interface then that local-remote IP pair becomes a real path that is used for forwarding.

In the topology in the above figure two groups are defined.

  1. mpls-group
  2. Internet-group

Further if paths need to be restricted through the Internet, the Internet groups can be divided into more groups. For example, the customer can define ISP1 and ISP2-ISP3 as separate groups create 2 Internet paths instead of 4.