MPLS route is still active in routing table even its corresponding OSPF route is not listed

[Ronie_Singh]

Hi There,

I found MPLS route is still active in routing table even its corresponding OSPF route is not listed in routing table.

Ori Destination Gateway Mtr Flags VLAN Duration
mp 192.17.80.55/32 172.17.79.1 1 U--D---um-L-- CR1-DR1_902 0d:2h:57m:41s
mp 192.17.80.55/32 172.17.79.85 1 U--D---um-L-- CR1-DR1_782 0d:3h:37m:45s
#or 192.17.80.55/32 172.17.79.85 12 UG-D---um--f- CR1-DR1_782 0d:3h:37m:46s

Even increasing the OSPF cost of the link, its mpls route is still active in routing table and traffic is going via that link.

How can I increase the metric of mpls route ?

Best Regards,
Ronie

[Stephane_Grosj1]

I double-checked with a real expert.

There are no OSPF Calculated routes here. If there were, there would be a lower case “L” instead of the uppercase one. MPLS next-hops may even not be turned on (since neither MPLS route is selected for routing, but do have a lower cost than the OSPF route). Can you confirm that?

The MPLS routes are ECMP here. This could be because OSPF reports both as equal cost, which I guess isn’t the case, since OSPF only shows one route, or it could also be due to adjacent nodes. Is CR1-DR1_902 connect directly to 192.17.80.55 from this node?

Can you share the output of "show mpls ldp peer detail"?

[Erik_Auerswald]

Hi,

I would expect the flags Lf for an active IP over MPLS route (using enable iproute mpls-next-hop) as in the following example:
#mp 10.0.0.2/32 10.1.0.2 1 U--D---um-Lf- t-s2-s3 0d:0h:1m:22s oa 10.0.0.2/32 10.1.0.2 14 UG-D---um---- t-s2-s3 0d:0h:14m:58s
It seems to me as if only the OSPF route is used for IP forwarding in the question above.

Thus the problem seems to be more that there are two LSPs available and possibly advertised via LDP, while only one LSP corresponding to the least cost path is expected.

This leaves the question of why there is the other LSP corresponding to a non-least cost path.

Thanks,
Erik

[Ronie_Singh]

The question being is why following mpls route is shown in routing table in the first place ?

mp 192.17.80.55/32 172.17.79.1 1 U--D---um-L-- CR1-DR1_902 0d:2h:57m:41s

Since there is only one ospf route (best route) is selected, there should be only one mpls route with the same next-hop (as in ospf route).

Your further explanation on this would be highly appreciated.

[Stephane_Grosj1]

Oh, then yes, I think so, you are telling the OS to use the MPLS LSP with that command. Check the User Guide (p.1222 in the 22.6 version) for "OSPF Calculated LSP Next Hops" for more details.

[Ronie_Singh]

Let me elaborate. Even only the single OSPF route is there, the path is chosen based on the mpls routes. There are two mpls routes as you can see in the output shared above, the first mpls route is taken as primary active path (its corresponding OSPF route is not even shown in routing table).

Is that due to the reason the cmd "enable ospf mpls-next-hop" is applied on the node ? Your further explanation on this would be highly appreciated.