Profile 27 w/ FRR

Coming from the previous lab, configure the Tree SID to use FRR TI-LFA.

Answer

#XR9
pce
 segment-routing
  traffic-eng
   p2mp
    policy Tree-SID-Pol1
     fast-reroute lfa

#XR1-XR8
group ISIS
 router isis '1'
  interface 'Gigabit.*'
   address-family ipv4 unicast
    fast-reroute per-prefix
    fast-reroute per-prefix ti-lfa

Explanation

To be able to use LFA with P2MP Tree-SID policies, we must first enable TI-LFA everywhere. This is done easily using the above group configuration. TI-LFA is added to every Gigabit interface.

#XR1-XR8
group ISIS
 router isis '1'
  interface 'Gigabit.*'
   address-family ipv4 unicast
    fast-reroute per-prefix
    fast-reroute per-prefix ti-lfa

Next we simply enable FRR LFA on the policy. Since this is a static policy, we do this on the PCE.

#XR9
pce
 segment-routing
  traffic-eng
   p2mp
    policy POL1
     fast-reroute lfa

Let’s look at a transit node such as XR1. Before making this change, the outgoing interface is explicit. The nexthop is the router’s IP address on the link. These are both signs that FRR is not in use for this P2MP policy.

After making the change, we can see on the PCE’s policy that FRR is enabled. All of the nexthops now have an exclamation point, indicating that FRR is in use.

On XR1, we now see no outgoing interface. The nexthop is now the node’s RID, and it has an exclamation point. This indicates that the IP FRR for the nexthop dictates the outgoing interface now.

Under normal circumstances, the direct link to R3 is used. But under FRR protection conditions, the multicast traffic is tunneled to R3 via the link to R2 (Gi0/0/0/0.3012).

The backup path will push two labels on top of label 15001: {16004/16003}.