Hi All !
I have a question regarding IGP (OSPF or ISIS) link-protection and ECMP.
Topology is triangle where R1 is connected to R2 and R3, and R2 to R3.
On R1 when node-link-protection is not configure, I will have only one route to reach the R2's loopback :
schalal@VR-DEVICE.re0:R1# run show route table inet.0 10.200.1.2/32
inet.0: 365 destinations, 691 routes (365 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.200.1.2/32 *[IS-IS/18] 00:00:17, metric 10
> to 10.200.112.2 via ge-0/0/1.112
but when I configure node-link-protection, I have two routes to reach R2's loopback :
schalal@VR-DEVICE.re0:R1# run show route table inet.0 10.200.1.2/32
inet.0: 365 destinations, 691 routes (365 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.200.1.2/32 *[IS-IS/18] 00:19:55, metric 10
> to 10.200.112.2 via ge-0/0/1.112
to 10.200.113.3 via ge-0/0/1.113
So primary path is R1=>R2, backup path is R1=>R3=>R2
Until there no problem. But what about ECMP ? It seems I can enable ECMP between the primary and backup path. But why the backup path has the same metric as the primary ? the path is longer which make the cost higher !
Let's try ECMP, but here is the output before ECMP :
schalal@VR-DEVICE.re0:R1# run show route forwarding-table destination 10.200.1.2/32
Logical system: R1
Routing table: default.inet
Internet:
Destination Type RtRef Next hop Type Index NhRef Netif
10.200.1.2/32 user 1 10.200.112.2 ucst 14084 23 ge-0/0/1.112
[edit]
schalal@VR-DEVICE.re0:R1# show routing-options forwarding-table
export [ LB ];
schalal@VR-DEVICE.re0:R1# run show route table inet.0 10.200.1.2/32
inet.0: 365 destinations, 691 routes (365 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.200.1.2/32 *[IS-IS/18] 00:00:07, metric 10
> to 10.200.112.2 via ge-0/0/1.112
to 10.200.113.3 via ge-0/0/1.113
schalal@VR-DEVICE.re0:R1# run show route forwarding-table destination 10.200.1.2/32
Logical system: R1
Routing table: default.inet
Internet:
Destination Type RtRef Next hop Type Index NhRef Netif
10.200.1.2/32 user 1 ulst 1048614 8
10.200.112.2 ucst 14084 11 ge-0/0/1.112
10.200.113.3 ucst 14057 15 ge-0/0/1.113
As you can see ECMP is active for the route to R2's loopback although the theoretical metric for the primary and backup path are different.
My question is : Do we have ECMP (when policy is configured on the forwarding-table) active when we enable IGP node-link-protection even if the theoretical cost of the primary and backup path are different ? Why ???
Thanks for you help