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New Member

Three ISP - Three Edge Routers - iBGP Mesh

iBGP-setup-Three-Service-Providers.JPG

Currently I have two service providers and two edge routers. RTR1 is iBGP peered to RTR2 and RTR2 is iBGP peered to RTR1. We are planning to install a third service provider and install RTR3. Making sure I have my iBGP mesh setup properly, and also considering "Three Different Service Providers" configurations aren't typically found with Google search can I get some feedback on the topo above? Seems simply but didn't want to run into any gotcha moments on deployment day!

RTR1 -> RTR2 | RTR1 -> RTR3

RTR2 -> RTR1 | RTR2 -> RTR3

RTR3 -> RTR1 | RTR3 -> RTR2

4 REPLIES
New Member

Re: Three ISP - Three Edge Routers - iBGP Mesh

Yep ibgp peers as full mesh as they are all ebgp peers as well. Any more and you would be better with one as a route reflector

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Three ISP - Three Edge Routers - iBGP Mesh

Hi,

Yes, you got it perfect for iBGP mesh.

However, if your are using any other IGP between your CE, then I would suggest disable bgp syncronization.

Also,

Are all 3 CE connected to same LAN segment or are they catering different.

If they are connected to same LAN segment, then you can use GLBP to load balance across 3 links.

HTH,

Smitesh

Three ISP - Three Edge Routers - iBGP Mesh

Hi,

I'd be careful here.

GLBP might be nice for outgoing traffic load sharing if a LAN with PCs is connected.

But in this case it's not so easy:

a) even when a PC is using one router as it's default gw, the router can still forward the traffic to another iBGP neighbor here if receiving a better route via iBGP,

b) traffic returning to the PC can take a different router (=link) on the returning path.

So an asymmetric routing can occur here easily - this is the true challenge in topologies like this.

I even don't see in the topology description:

Is this connecting the LAN to the Internet or some entreprise backbone?

If enterprise, are there some sites connnected to multiple providers or any kind of gateways between them?

HTH,

Milan

Three ISP - Three Edge Routers - iBGP Mesh

Hi ,

I can see that you are using HSRP between RTR1 and RTR2 and the RTR3 is the third in the group so at any given time you have a primary /back up situation. so thats good in terms of redundancy.

now coming to BGP.

make sure to have local pref and AS-path prepend configured correctly so tht you dont end up with assymetic routing.

other than that it should be fine.

for eg: RTR 1- local pref 140

         RTR2  - local pref 120 , as-path prepend

          RTR3 - local pref 110 , as parth prepend

so routing is consistent

HTH

Kishore

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