cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
983
Views
0
Helpful
6
Replies

second label in mpls vpnv4

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.

1 Accepted Solution

Accepted Solutions

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

View solution in original post

6 Replies 6

rais
Level 7
Level 7

The outer label guides the packet to the router. The inner one guides it to the right inerface it should exit.

HTH.

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?

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

But if we have PHP enabled?

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.

Harold Ritter
Spotlight
Spotlight

Hi Volodymyr,

The second label is used on the egress PE to decide which egress VRF interface the packet should be forwarded to.

Regards

Review Cisco Networking for a $25 gift card