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MPLS Traffic Load Sharing

Unanswered Question
Aug 10th, 2006
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What is the best way to configure a load sharing policy from multiple CE "remotes" to two CE "hosts" in a MPLS network? Currently, all incoming traffic goes to only one host from the PE.

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mheusinger Thu, 08/10/2006 - 07:45
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Hi,


you need to have a look at the complete routing architecture to understand possibilities/responsibilities.


Mainly load distribution for a single prefix can only occur, if more than one path to a destination is known. This however might not be given in the MPLS network. The underlying reason is that BGP will only send the best path in an update - but not all pathes a BGP speaker knows of (RFC mandates this).


As practically all larger BGP implementations use Route Reflectors, which are (RFC conforming) BGP speakers, they will only forward the best path to a destination. The result is:

IF more than one path to a destination network exists and is sent to the RR through different PE routers (with same RD) then only one path will be distributed to all other PE routers.


In this scenario load sharing for a single prefix can not occur, because only one routing table entry exists for this prefix in most if not all PE routers. All you can do is to try to load share by selecting different pathes for different destination prefixes by influencing routing metric. This way part of your traffic will go one way and part will take another path.


IF the SP however uses different RD values for every VRF and the proper "maximum-path" statements in MP-BGP, then load sharing per prefix can be achieved in the MPLS network. The customer however can not influence the SP setup.


Hope this Helps! Please rate all posts.


Regards, Martin

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