bpg and mpls

Unanswered Question
Jun 24th, 2008

I read that mpls engineering requires a link state routing protocol such as ospf or isis. We will be going to mpls soon, but currently use bgp on our WAN. Since bgp is a path vector protocol, does that mean we will need to drop bgp in favor os something like ospf or isis?

thank you,

Bill

I have this problem too.
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Harold Ritter Tue, 06/24/2008 - 13:58

Bill,

Going to MPLS doesn't necesseraly means using MPLS Traffic Engineering. Also, if you ever need to use MPLS TE, you can always deploy MPLS TE InterAS solutions.

Regards,

WILLIAM STEGMAN Thu, 06/26/2008 - 12:55

Does that mean it will work, but in a sort of degraded fasion? Will we be able to utilize the label switching, quasi layer 2 performance mpls offers using BGP?

I should add a few details regarding our network. This is a WAN using a private AS. We use bgp to advertise networks across the WAN. I'm not sure what's running in the provider's network. Perhaps they are using a link state routing protocol in their core and this is not actually an issue. I will have to follow up with the provider.

thanks everyone.

adam.wilkins Wed, 06/25/2008 - 20:59

You can run MPLS with any routing protocol as the IGP. I've implemented it with EIGRP recently. However, the traffic engineering component of MPLS does requires a link state protocol like ISIS or OSPF. This is because CSPF which is used to set up the paths uses the information in the link state database. The entire topology (at least for that area or level) has to be known. You have to do a few different things to get TE paths to traverse areas/levels e.g. loose route objects.

shivlu jain Thu, 06/26/2008 - 00:18

bill

your question is very good but BGP is used to carry the large ip routes which your igp cannot do. But in the MPLS network we use BGP to carry the customer routes from one pe to another transparently. If you donot use the bgp to transport the routes then may be the customers routes will be carried by your igp and which is not feasible becasue ip overlapping cannot be done in that case. Thats why we require the BGP in mpls network for carring customers routes and IGP for carrying SP routes. Fr every Customer route the next hop will be the SP cloud and whcih can be reached by only IGP.

regards

shivlu

s.ganguly Thu, 07/17/2008 - 06:50

Hi Kalpana,

There are some good references for this:

1) MPLS & VPN Architectures I & II by Pepelnjak et. al.

2) MPLS Enabled Applications by Ina Minei

cheers

santanu

s.ganguly Thu, 07/17/2008 - 06:46

Hi Bill,

Normally MP-BGP is used for implemenattion of MPLS in backbone or core. As pointed out by hritter and shivlu, often BGP is run on top of an IGP (something like ISIS or OSPF) for reasons of transperancy for customers. If you are NOT using MPLS TE, then options can be various.

Cheers

santanu

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