MPLS TE - Link and Node Protection

[amit.bhagat]

Hi Guys,

Just revisiting an old topic again - MPLS-TE Link and Node Protection.

Is it enough that the backup path (facility backup as supported by IOS) just merge on any LSR of the protected LSP? It does seem to be that way. For example, consider the following topology -

R1-------R2-------R3------R4------R6

            |_____R5____|

The Primary LSP is setup with explicit path R1-R2-R3-R4-R6 and requesting Link-Protection.

R2 protects the link R2-R3 with a backup LSP which has an explicit path R2-R5-R4. The backup LSP merges on the Primary LSP but R4 is not the next-hop to R2 protecting the primary LSP.

This works in my testing but my understanding was that for-

Link Protection - the backup LSP must be terminated on the LSR which is next-hop to the LSR protecting the primary LSP

Node Protection - the backup LSP must be terminated on the LSR which is next-next-hop to the LSR protecting the primary LSP

Your thoughts?

Regards,

Amit.

[Marwan ALshawi]

Your understanding is correct

This is node protection not link

If r5 terminate on r3 then it will be links protection

[amit.bhagat]

Hi Marwan,

Thanks for replying. I guess the point I was trying to make was this-

Consider in the above topology, there is another link between R3 and R5 as well. Now, R2 creates another backup tunnel (Tunnel-2000) to R3 with explicit-path R2-R5-R3 to protect the link R2-R3.

In this case, even if R1 is requesting local-protection, R2 still chooses the backup-tunnel which has the explicit-path R2-R5-R4 (Tunnel-1000) to protect the primary LSP, rather than Tunnel-2000 which has the explicit-path R2-R5-R3.

I am just trying to understand why Tunnel-1000 is preferred over Tunnel-2000 by R2 to protect the primary LSP - no matter how bad Tunnel-1000 metric be. Also, there is no autoroute announce on backup tunnels.

Regards,

Amit.

[Marwan ALshawi]

NHOP Versus NNHOP Backup Tunnels

More than one backup tunnel can protect a given LSP, where one backup tunnel terminates at the LSP

’

s

NNHOP, and the other terminates at the LSP

’

s NHOP. In this case, the router chooses the backup tunnel that

terminates at the NNHOP (that is, FRR prefers NNHOP over NHOP backup tunnels)