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Silver

Understanding Multiprotocol BGP

Could someone please explain Multiprotocol BGP, especially in relation to carrying VPN version 4 addresses. I'm wondering how it is used outside the MPLS implementation and how a non-MPLS router running MBGP can send VPNv4 routes to a MPLS PE router. I hope someone understand a bit of what I'm saying, any info though will be appreciated.

3 REPLIES
Gold

Re: Understanding Multiprotocol BGP

I'm not entirely positive about what you are asking, but.... I'm guessing you're asking about how VPNv4 routes could pass through a non VPNv4 BGP speaker--is that correct? For instance, if you have a route reflector that's not running VPNv4, how can it pass the routes on to the PE routers?

It couldn't, because the VPNv4 information is carried in a separate AFI/SAFI pair than normal BGP prefixes. A BGP speaker that doesn't understand MBGP at all would simply not accept these AFI/SAFI's. When the two peers negotiate capabilities, the MBGP AFI/SAFI for VPNv4 prefixes would not be negotiated, so they wouldn't be exchanged.

Does this answer the question, or is there some other issue you are thinking about?

Russ.W

PS Make certain you put BGP in your reply, if you reply with more questions, otherwise I won't see it. :-)

Silver

Re: Understanding Multiprotocol BGP

Yes, but got more questions. If I was not using route reflectors, could I get the BGP neighbours to exchange vpnv4 routes, when they are not directly connected? What place does VPNv4 addresses have in routing, outside the implemenvtation of MPLS? Could I possibly design a form of Virtual Private Network based on the VPNv4 addresses, and could it be carried across the internet, a long throw.

I've been looking for documentation on vpnv4 and MBGP but can seem to get anything. Could you help?

Gold

Re: Understanding Multiprotocol BGP

Yes you could get two iBGP peers to exchange vpnv4 routes although they are not directly connected--but it's rather sticky to get the routers in the middle to route traffic it doesn't have routes for--the normal "network in the middle" problem that BGP originally tried to deal with using synchronization, but instead we deal with by running BGP everywhere, using route reflectors, etc.

You could designa vpn using vpvnv4 addresses, but you would have to make certain every service provider in the path was going to accept, and carry the routes all the way through.

For more information on MBGP, see:

http://www.cisco.com/en/US/tech/tk365/tk859/tech_protocol_family_home.html

http://www.cisco.com/en/US/tech/tk365/tk859/tech_technical_documentation.html

I couldn't find a lot on multiprovider MPLS tunnels on the web--it's mostly just a matter of getting the service providers to run RFC2547bis, I think.

Russ.W

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