OSPF route path-id

[Mohit Sahai]

In the below output what exactly is "path-id"

RP/0/RSP0/CPU0:ASR9006-P2#sh ospf vrf TR-VRF-1-1 routes         
Wed Jul  3 07:26:38.194 UTC

Topology Table for ospf 8, VRF TR-VRF-1-1 with ID 100.0.1.2

Codes: O - Intra area, O IA - Inter area
       O E1 - External type 1, O E2 - External type 2
       O N1 - NSSA external type 1, O N2 - NSSA external type 2

O    31.31.0.0/24, metric 1
       31.31.0.1, directly connected, via TenGigE0/0/1/2.1
O E2 200.0.0.1/32, metric 0
       31.31.0.2, from 192.0.0.1, via TenGigE0/0/1/2.1, path-id 1
O E2 200.0.0.2/32, metric 0


Thanks,
Mohit

[Martin L]

I am curious myself as wel. is this XR ios ?

[Mohit Sahai]

Yes its in ios xr

[Giuseppe Larosa]

Hello Mohit,

I have found another example of a show ospf route that includes a path-id1 field here

https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k-r6-3/routing/command/reference/b-routing-cr-asr9000-63x/b-routing-cr-asr9000-63x_chapter_0110.html#wp1714883199

Unfortunately, there is no explanation of the specific field. However, in that case path-id 1 is associated to the primary route and also a backup route using topology indipendent LFA is listed.

In your case you are looking at OSPF routes in a VRF and the field appears for an O E2 route and my guess is that the path-id 1 refers to the OSPF path to the ASBR that originated the O E2 type 5 LSA.

At first, I was thinking you have MPLS TE used for this MPLS L3 VPN in the forwarding plane, but path-id 1 looks like strange to refer to an MPLS TE tunnel identifier.

Hope to help

Giuseppe

[Georg Pauwen]

Hello,

in a lot of Cisco docs, path-id is just the phyiscal numbering of the interface. So in e.g.:

interface GigabitEthernet 0/0/0/0

0/0/0/0 would be the path id. I wonder if 'path-id 1' in your case could be related to the numbering of the subinterface. If that is the case and you add another subinterface .2, the path-id should be 2. Not sure if you are in a position to test that...

Strange that it appears only on the E2 route though...