SR-TE policies, explicit paths and binding SIDs

Fellgate Carrier's main path from R1 to R4 goes through R2. R3 is on a longer, lower-latency route that the IGP doesn't choose, and the product team wants one traffic class to use it. On a classic core that would mean RSVP-TE, with state on every router along the path. With SR-TE, only the headend knows there's a path: it writes the route into the label stack.

The four routers run IS-IS with SR, and MPLS TE is enabled, so tunnels can be built.

What this release can't do. XRv 6.3 builds SR policies and binding SIDs, but it doesn't steer BGP routes into a policy by colour, and a policy has no autoroute. So this lab steers with tunnel-te and with a binding SID. It also refuses an explicit binding SID inside the default local block, 15000 to 15999: the policy shows Error: already assigned, because the label manager holds that block. So this lab takes 30100 from the dynamic range. Colour and on-demand next hop (ODN) are described as concepts.