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Question on relation between MPLS and MPBGP


I'm working on MPBGP for a PhD and I need to well implement its routing scheme in a simulation environement.

To do that, I have a question which stay unsolved...

When a PE (say PE Src) learns a MPBGP route from another PE (say PE Dst), it check the community attributes of this route first. If this check pass, then the route is insert into the VRF of PE Src. During this insertion, 2 labels are insert with the route : the bottom label which identifie the sub network one can reach from PE Dst and the top label which identifie the LSP to reach PE Dst from PE Src.

What happen if several LSPs (with different FEC) exist between PE Src and PE Dst ?

More precisely, how PE Src knows which LSP will be used to reach PE Dst ?

And what happen if no LSP exists ?

I hope someone may answer this question. I read manu documents about MPBGP and I read RFC too but I didn't find anything about this issue.

Have a good day.

Sincerely yours.



Re: Question on relation between MPLS and MPBGP

Use the show IP BGP command to view the path selected. There are list of parameters which decides this. All the other things remains same its the first route which is selected .

Community Member

Re: Question on relation between MPLS and MPBGP

Hi, thanks for your answer first

In fact, I can't use Cisco commands as I'm trying to model VPN routing scheme in a simulator for my PhD.

Could you give me some precisions about this list of parameters which decides the LSP choice ?


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