Example: Enabling BGP ECMP for BGP/MPLS VPN EBGP

You can create a mixed ECMP environment in which both EBGP and IBGP paths are selected as multipaths and used for load balancing. Doing this enables the E Series router to take into account both EBGP VPN routes learned from a CE router device and IBGP VPN routes learned from a remote PE device when determining load balancing.

In Figure 95, a BGP/MPLS network connects PE 1 and PE 2, which are configured for VPNv4 unicast IBGP peering. CE 1 and CE 2 are configured for EBGP peering with the PE devices. CE 2 is multihomed, connected to both PE 1 and PE 2.

Figure 95: BGP/MPLS VPN EIBGP Example

VRF A has two paths to get to CE 2: the IBGP path through the MPLS network, and the EBGP path by means of regular IP.

To support BGP/MPLS ECMP, PE 1 is configured with the maximum-paths eibgp command in the IPv4 unicast VRF A address family. Doing this allows both the EBGP paths from CE 2 and the IBGP paths from PE 2 to be selected as multipaths in the VRF A routing information base (RIB) for use in load balancing.

Traffic taking the various routes from CE 1 to CE 2 is treated as follows:

• Traffic from CE 1 to CE 2 that takes the EBGP route from PE 1 is forwarded as IP packets.
• Traffic from CE 1 to CE 2 that takes the IBGP route from PE 1 is forwarded as MPLS-encapsulated packets. PE 2 receives the MPLS-encapsulated traffic from PE 1, removes the encapsulation, and then forwards the traffic as IP packets by means of the EBGP route to CE 2.