Is it possible to use LFA in IS-IS for broadcast links? Neighbours reachable via P2P links are used for repair-paths but broadcast links are not used at all.
CSR1#sho isis rib 184.108.40.206/32 prefix attr X:0 R:0 N:1 [115/L1/30] via 192.168.13.3(GigabitEthernet2), from 220.127.116.11, tag 0, LSP[4/9/68] prefix attr: X:0 R:0 N:1 (installed) [115/L2/30] via 192.168.13.3(GigabitEthernet2), from 192.168.13.3, tag 0, LSP[15/15/56] prefix attr: X:0 R:1 N:1 [115/L2/30] via 192.168.13.3(GigabitEthernet2), from 18.104.22.168, tag 0, LSP[15/14/62] prefix attr: X:0 R:0 N:1 [115/L2/31] via 192.168.12.2(GigabitEthernet1), from 192.168.24.2, tag 0, LSP[16/16/60] prefix attr: X:0 R:1 N:1 [115/L2/50] via 192.168.11.11(GigabitEthernet3), from 22.214.171.124, tag 0, LSP[11/11/67] CSR1#sho isis neighbors System Id Type Interface IP Address State Holdtime Circuit Id CSR2 L1 Gi1 192.168.12.2 UP 22 CSR1.01 CSR3 L1 Gi2 192.168.13.3 UP 26 CSR1.02 CSR1#sho ip ro repair-paths Gateway of last resort is not set 126.96.36.199/32 is subnetted, 1 subnets i L1 188.8.131.52 [115/30] via 192.168.13.3, 01:06:43, GigabitEthernet2 interface GigabitEthernet1 ip address 192.168.12.1 255.255.255.0 ip router isis end ! interface GigabitEthernet2 ip address 192.168.13.1 255.255.255.0 ip router isis
CSR1#sho run | s router isis
fast-reroute per-prefix level-1 all
fast-reroute per-prefix level-2 all
When I change interface type to P2P, repair-path are installed.
what you have seen is interesting.
the most current RFC about selection of LFA alternate next-hops should be
in a point to point link a pre calculated next-hop is available if the p2p link is alive and cannot change.
In a broadcast network each IS node is adjacent with the pseudo node DIS, so a pre-defined IP next-hop for a prefix may not be available. In practice, the pseudonode might be seen as third party or not providing first hand information.
Also in broadcast link IS IS use LAN hellos different for level-1 and level-2 and actually level 1 DIS and level 2 DIS can be different nodes.
Hope to help
This RFC describes the common behavior for IGP. OSPF works fine on bcast network type. IS-IS on the other hand exhibits inability to do so far. Could it be a bug? Or there is smth needed in config?