link protection using MPLS

[sarahr202]

Hi everybody

I am reading a book on MPLS TE by  Eric Osbornne and Ajay .

I have a question

R1------R2---(cloud)----R4

Please consider the following config:

R1

tunnel 0

ip unnumbered L0

tunnel destination ( 4.4.4.4)

tunnel mode mpls traffic -engineering

tunnel mpls traffic-engineering bandwidth 40

tunnel mpls traffic-engineering path-option 10 dynamic.

tunnel mpls traffic-engineering fast-reroute

Assuming 40 mig is available but R2 is not configured  to provide any protection that R1 is asking for.

Will tunnel 0 come up though requested protection is not provided?

Thanks

[Nagendra Kumar Nainar · Accepted solution]

Hi,

The tunnel will come up. When you enable "tunnel mpls traffic-engineering fast-reroute", the head end will set the link protection required flag in PATH message along with record-route.

So each router along the path will include its router id and label in RESV message which can be used by any PLR to detect the merge point (using RID) and use the label to merge the backup tunnel.

In short, the presence of "fast-reroute" configuration will not affect the primary tunnel status.

-Nagendra 

[aqeel ahmed]

Fast-reroute signals along the path to protect the tunnel where protection is enabled but this is not a mandatory requirement so tunnel will come up.

Protection comes in play when you identify some link in your network may go down and want to provide a backup for all fast-reroute enabled LSPs going through that link. if configured for protection then as soon as that link goes down, all protected tunnels will be rerouted on backup tunnel/path until head-end calculates a new shortest Path using running CSPF.