Route selection across EVPN-IFL and other owners in the VPRN service

This section describes the rules for route selection among EVPN-IFL, VPN-IP, and IP route table owners.

A PE may receive an IPv4 or IPv6 prefix in routes from different or same owners, and from the same or different BGP peer. For example, prefix 10.0.0.0/24 can be received as an EVPN-IFL route and also received as a VPN-IPv4 route. Or prefix 2001:db8:1::/64 can be received in two EVPN-IFL routes with different route distinguishers from different peers. In all these examples, the router selects the best route in a deterministic way.

For EVPN-IFF route selection rules, see Route selection for EVPN-IFF routes in the VPRN service. In SR OS, the VPRN route table route selection for all BGP routes, excluding EVPN-IFF, is performed using the following ordered, tie-breaking rules:

1. valid route wins over invalid route

2. lowest origin validation state (valid<not found<invalid) wins

3. lowest RTM (route table) preference wins

4. highest local preference wins

5. shortest D-PATH wins (skipped if d-path-length-ignore is configured)

6. lowest AIGP metric wins

7. shortest AS_PATH wins (skipped if the as-path-ignore command is configured for the route owner)

8. lowest origin wins

9. lowest MED wins

10. lowest owner type wins (BGP<BGP-LABEL<BGP-VPN)

    Note: BGP-VPN refers to VPN-IP and EVPN-IFL in this context.

11. EBGP wins

12. lowest route table or tunnel-table cost to the next hop (skipped if the ignore-nh-metric command is configured)

13. lowest next-hop type wins (resolution of next hop in TTM wins vs RTM) (skipped if the ignore-nh-metric command is configured)

14. lowest router ID wins (skipped if the ignore-router-id command is configured)

15. shortest cluster_list length wins

16. lowest IP address

    Note: The IP address refers to the peer that advertised the route.

17. EVPN-IFL wins over IPVPN routes

18. next-hop check (IPv4 next hop wins over IPv6 next hop, and then lowest next hop wins)

    Note: This is a tiebreaker if BGP receives the same prefix for VPN-IPv6 and IFL. An IPv6-Prefix received as VPN-IPv6 is mapped as IPv6 next hop, whereas the same IPv6 prefix received as IFL could have an IPv4 next hop.

19. RD check for RTM (lowest RD wins)

ECMP is not supported across EVPN-IFL and other owners, but it is supported within the EVPN-IFL owner for multiple EVPN-IFL routes received with the same IP prefix. When ECMP is configured with N number of paths in the VPRN, BGP orders the routes based on the previously described tie-break criteria breaking out after step13 (lowest next-hop type). At that point, BGP creates an ECMP set with the best N routes.

Example:

In a scenario in which two EVPN-IFL routes are received on the same VPRN with same prefix, 10.0.0.0/24; different RDs 192.0.2.1:1 and 192.0.2.2; and different router ID, 192.0.2.1 and 192.0.2.2; the following tie-breaking criteria are considered.

• Assuming everything else is the same, BGP orders the routes based on the preceding criteria and prefers the route with the lowest router ID.

• If vprn>ecmp=2, the two routes are treated as equal in the route table and added to the same ECMP set.