Using SR-MPLS in FIB

In this chapter, the integration of SR into an existing traditional MPLS network has been explored. Two distinct methods are used to establish parallel label-switched paths. The FIB currently favors LDP labels over SR-MPLS labels, even though both LSPs are available. We will now adjust the FIB to prioritize SR for IP to MPLS traffic.

Configuration

The left half of the topology (Figure 3.1) is now capable of forwarding labeled traffic using both LDP and SR-MPLS for MPLS-to-MPLS traffic.

The default method for forwarding IP-to-MPLS traffic remains LDP, but it can be altered with the following configuration.

On SR-MPLS routers

The routers PE1, P2, P3, P6, and P7 within the SR-MPLS domain will now be configured with sr-prefer to prioritize SR-MPLS labels in the FIB:

router IS-IS IGP
address-family ipv4 unicast
  segment-routing mpls sr-prefer

sr-prefer is important only on the label edge routers. This is because the core routers will swap...