Friday, June 5, 2009

Path Resv Messages

I wrote in the previous post about traffic engineering, how it could help to utilize the secondary link in case when primary link is congested. MPLS TE is used set up the tunnels from headend to tailend routers. Intermediate routers are only responsible to forward the tarffic. MPLS TE uses RSVP signalling which is aka Resource Reservation Protocol. It uses two messages to acomplaish this signaling: Path Messages & Resv Messages.


According to the picture, R1 wants to set up the an MPLS TE with R3. R1 sends the path messages along the path to reserve the resources. If the requested resources are not available than router sends a message back to the requested router which is ingress router and it look for the another path. If another path is not available then in that case it would fail to establish the MPLE TE. MPLS TE signaling always flow from ingress router to egress router with path messages and labels distribution occured from egress to ingress with resv messages.

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