[c-nsp] MPLS Backup Tunnels

[alaerte.vidali at nsn.com]

Would you comment the benefits and disadvantages of configuring backup
bandwidth statement on backup tunnel?

tunnel mpls traffic-eng backup-bw xxx

I have seen networks using it and other networks not using it.

according to some Cisco docs and SE advice, it should be configured
backup bandwidth even when backup tunnel is signaled with zero
bandwidth.

Cisco says:

Signaled Bandwidth Versus Backup Bandwidth

Backup bandwidth is used locally (by the router that is the headend of
the backup tunnel) to determine which, and how many, primary LSPs can be
rerouted on a particular backup tunnel. The router ensures that the
combined bandwidth requirement of these LSPs does not exceed the backup
bandwidth.

Therefore, even when the backup tunnel is signaled with zero bandwidth,
the backup bandwidth must be configured with the value corresponding to
the actual bandwidth requirement of the traffic protected by this backup
tunnel. Unlike the case when bandwidth requirements of the backup
tunnels are explicitly signaled, the value of the signaled bandwidth
(which is zero) is not the same value as the backup bandwidth. 

Any comments, concerning if you normally use or not backup bandwidth
command under backup tunnels and pros and crons?


Tks,
Alaerte