Resolving unlabeled IPv4 BGP routes to segment routing policy tunnels

About this task

For an unlabeled IPv4 BGP route to be resolved by an SR policy:

Note: Contrary to section 8.8.2 of draft-filsfils-segment-routing-05, BGP only resolves a route with multiple color-extended communities to an SR policy using the color-extended community with the highest value.

As an example, if under these conditions, there is an IPv4 route with a color-extended community (value C) and a specific BGP next-hop address, the order of resolution is as follows:

Procedure

  1. If there is an SR policy in TTMv4 for which end-point = BGP next-hop address and color = Cn, then use this tunnel to resolve the BGP next hop.
  2. If no SR policy is found in the previous step and the Cn color-extended community has its color-only (CO) bits set to '01' or '10', then try to find in TTMv4 an SR policy for which endpoint = null (0.0.0.0) and color = Cn. If there is such a policy, use it to resolve the BGP next hop.
  3. If no SR policy is found in the previous steps and the Cn color-extended community has its CO bits set to '01' or '10', then try to find in TTMv6 an SR policy for which endpoint = null (0::0) and color = Cn. If there is such a policy, use it to resolve the BGP next hop.
  4. If no SR policy is found in the previous steps but there is a non-SR policy tunnel in TTMv4 that is allowed by the resolution options and for which endpoint = BGP next-hop address (and for which the admin-tag meets the admin-tag-policy requirements applied to the BGP route, if applicable) then use this tunnel to resolve the BGP next hop if it has the highest TTM preference.
  5. Otherwise, fall back to IGP, unless the disallow-igp option is configured.
Parent topic: Resolving BGP routes to segment routing policy tunnels