Resolving unlabeled IPv6 BGP routes to segment routing policy tunnels

About this task

For an unlabeled IPv6 BGP route to be resolved by an SR policy:

A color-extended community must be attached to the IPv6 route.
The base instance BGP next-hop-resolution configuration of shortcut-tunnel>family ipv6 must allow SR policy tunnels.

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.
For AFI2/SAFI1 routes, an IPv6 explicit null label should always be pushed at the bottom of the stack if the policy endpoint is IPv4.

As an example, if under these conditions, there is an IPv6 route with a color-extended community (value C) and a BGP next-hop address, the order of resolution is as follows:

Procedure

If there is an SR policy in TTMv6 for which endpoint = the BGP next-hop address and color = Cn, then use this tunnel to resolve the BGP next hop.
If no SR policy is found in the previous step and the Cn color-extended community has its CO bits set to '01' or '10', then try to find a SR policy in TTMv6 for which endpoint = null (0::0) and color = Cn. If there is such a policy, use it to resolve the BGP next hop.
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' and there is an SR policy in TTMv4 for which endpoint = null (0.0.0.0) and color = Cn, then use this tunnel to resolve the BGP next hop.
If no SR policy is found in the previous steps but there is a non-SR policy tunnel in TTMv6 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.
Otherwise, fall back to IGP, unless the disallow-igp option is configured.