MPLS Label

Unanswered Question
Jan 22nd, 2008

which route or update will have MPLS assignment?





I read that BGP updated route or prefix will not have the label assignement.....why?

I have this problem too.
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yagnesh_tel Tue, 01/22/2008 - 20:30

In MPLS, the criteria for assigning/creating labels for routes/updates does not depend on source(protocol) of that update. MPLS will generate labels for each and every IP prefix presents in the routing table irrespective of its source.

The answer of your second question lies in the question that what IGP can offer which BGP can't offer for running MPLS. FYI, it is mandatory to have IGP running in your network in order to configure MPLS as MPLS has to rely on IGP to construct its label forwarding table. Whereas in general, BGP is required for its ability to deliver routing information between routers that are not directly attached. So the fact is BGP itself somewhat relies on IGP for peer reachability at least at micro-level. So how can you expect MPLS to build its forwarding table from BGP routing table?


jordanbauduin Wed, 01/23/2008 - 03:00

Indeed, BGP does a recursive lookup to resolve the next hop q

address which is known via your IGP. So MPLS does assign a label to the IGP entry which is your next-hop BGP.


dangal.43 Wed, 01/23/2008 - 09:14

But in Inter AS VPN topology we are chaning as well as assigning new label (VPN as well as MPLS labels) of prefiexes so if we change the VPN label then data will be part of other VPN then how both the PE on different ASs will have same VPN?

senthil_kumarpv Mon, 01/28/2008 - 04:49


what will happen is that ,when there is a label assignment in other PE (NNI ) , that ISP cloud will only know about the changed VRF ( Routing Context ) and will reach the destination once it came back to the NNI it will remove the new VRF and wear the old one so that local isp can route that packet.

There is different concept inter AS MPLS like Option A,Option B and Option C,what i have talked is Option A


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