MPLS vs. uRPF: What happens first

Klimkowski · ‎11-30-2011

If you enable unicast RPF strict and MPLS on a LER router, does the router first perform a the RPF lookup on the inbound packet? Or would the LER router push matching packets into a MPLS tunnel before the uRPF lookup?

Thanks!

Ben Klim

Peter Paluch · ‎11-30-2011

Hi Benjamin,

While I have not read this in any normative document, to me, the logic dictates that the uRPF shall be performed first, and only if the packet passes the check, it should be processed further. If the uRPF check fails, the packet shall be dropped, which means there is no point in pushing any labels to it or forwarding it further just because there is an MPLS LSP onto which the packet can be forwarded.

Why do you ask, anyway?

Best regards,

Peter