[c-nsp] MPLS FRR with auto-bw

[Vitaliy Karlov]

> can you clarify what you mean by "provide backup" for path AC via ABC?  
> 
> Looking at the picture alone I'm guessing: are you asking to only use
> the path ABC for the tunnel AC if the other tunnels crossing AB leave
> enough bandwidth for the AC tunnel? If tunnel AC bw requirements can't
> be met on link AB, then you want it to use the AC link?
> 
> If that's the case, you are asking for a) two path options on tunnel AC
> (the primary being the ABC path, the secondary the AC direct link, or
> dynamic if this is also the shortest path), and b) for different tunnel
> priorities so an increase in bandwidth of the "AB"-Tunnels could
> actually lead to tunnel AC using the ABC path being preempted. 
> 
> So if you configure the "couple of MPLS TE tunnels" crossing the link AB
> with "tunnel mpls traffic-eng priority 4 4" (or another number lower
> than the default of 7), they will preempt the AC tunnel if it is
> configured with the default 7 (lower number is higher priority).
> 
> If you mean some form of FRR, please clarify the exact requirements..


Oliver,

Thanks for the answer. I'll try to elaborate it a bit.

You are right, the very good option to solve it in the mentioned scenario is to use two (or more) different path options in the tunnel AC itself. I got it out of my head composing previous e-mail.

But if we would come back to FRR, the question still remains open. Lets say link AC has configured backup-path (mpls traffic-eng backup-path Tunnel3010). Tunnel3010 has explicit path-option via ABC (next-hop B, next-hop C). Without bandwidth requirements everything works very well - link AC fails, tunnel(s) crossed AC link is(are) rerouted via ABC. But the point is to keep backup tunnel (Tunnel3010, ABC) up and signalled only if the enough bandwidth available along the path ABC to provide backup facility to tunnel(s) crossed AC.

In other words, if AC (bw of crossed tunnels) + AB (bw of crossed tunnels) <= maximum throughput AB, tunnel3010 is up.

One option I see is to use lower priority (as you mentioned) and auto-bw in the backup tunnel (tunnel mpls traffic-eng auto-bw frequency 300). But the disadvantage is (in case of lack of capacity on the path ABC) the service degradation at least 300 sec (minimum value I can set) while backup tunnel recalculates and re-requests the bandwidth. But I guess it is a very wrong way and no one would follow it.

So, the question itself is how to provide bandwidth protection for tunnel(s) crossed path AC via ABC.

Hope it is a bit clear now.