06-27-2013 06:45 AM - edited 03-04-2019 08:19 PM
Hi.
I am new to L3VPNs and recently I have discovered that MPLS packet containing MP-BGP update has two labels. Inner one is distributed via MP-BGP.
But I dont understand why we need the second label? Please explain.
Solved! Go to Solution.
06-27-2013 07:42 AM
Hi Volodymyr,
The only lookup will take place in the lfib (the mpls forwarding table) and packet will be forwarded out the right egress interface. The CEF fib will not be looked up on the egress PE.
Regards
06-27-2013 07:22 AM
The outer label guides the packet to the router. The inner one guides it to the right inerface it should exit.
HTH.
06-27-2013 07:28 AM
You want to say that inner label says which instance of CEF to check? Because on data plane router has no idea about VRFs if there are no inner labels. I am right?
06-27-2013 07:42 AM
Hi Volodymyr,
The only lookup will take place in the lfib (the mpls forwarding table) and packet will be forwarded out the right egress interface. The CEF fib will not be looked up on the egress PE.
Regards
06-27-2013 07:58 AM
But if we have PHP enabled?
06-27-2013 08:00 AM
PHP is going to pop the outer label and leave the inside one intact. Otherwise, egress PE wouldn't know where to send the packet out.
Regards.
06-27-2013 07:24 AM
Hi Volodymyr,
The second label is used on the egress PE to decide which egress VRF interface the packet should be forwarded to.
Regards
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