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New Member

iBGP

Hi

We are going to do PEERING with the another ISP using iBGP.And there is four hop(routers) to reach the boarder router which will be use for peering.

Now should I run in all routers iBGP from gateway router to boarder router or just in Gateway and boarder router.

Please help me.

rgds

Ishwar

3 REPLIES
Silver

Re: iBGP

Logically you should be peering using eBGP, but if it's iBGP, you will need to fully-mesh or have reflectors/confeds. You will become part of your ISP's network.

If you run iBGP on border only, how will you tell other routers about routes learned? Redistributing to IGP can be dangerous or impossible depending upon number of prefixes you exchange. If you run it on border+gateways, how do you expect other routers to learn about all prefixes. Best solution is to eBGP with the ISP and iBGP all internal. You can also eBGP with ISP on border and redistribute to IGP if your number of prefixes exchagned is small.

Hope this helps.

New Member

Re: iBGP

Thanks a lot...but I am little bit confuse.

We have a gate way router with eBGP running with Singtel.Now we want to do peering with another ISP.

There is four hop two reach the boarder router.

NOw I understand that we have to run eBGP in boarder router.Now should I run BGP in all four routers or not.OSPF is running in our network.

Will you please suggest me.

regards

Ishwar

Silver

Re: iBGP

I assume the border router you are talking about is your border router (not your ISP's). In this new, dual-homed scenario you have two options:

1. Simply redistribute eBGP routes to OSPF, as you might be already doing with Singtel. This option is ok if number of prefixes your are sharing are few.

2. Run iBGP on all of your internal routers. This option will handle large number of prefixes, again depending you have enough resources in your network.

You need to implement one or the other option to dynamically divert traffic when one of the ISPs fail. You may also have to tune traffic symmetry.

If there are four hops between your border and newISP border router, then you dont need to run BGP on them, you can multi-hop.

Regards.

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