Re: [isp-bgp] Size of iBGP Mesh

[David Sinn <dsinn@...>]

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That may not always be the case with a iBGP mesh as it will depend on  
your best path decision.

Your eBGP speaking routers should only be passing on routes they  
consider best, and thus only pass on a subset of the RIB as they see  
it.  Nominally Local-Pref, AS-Path & MED should allow your border  
routers to make this decision and cull out some of the RIB entries.   
If, on the other hand, the best path decision is falling down to IGP  
metric or some other local decision in your core, each border router  
will be passing on those similar prefix's because each considers  
their own best and your router deeper in your network needs to make  
it's own best decision.

Most look to deploy route-reflection because of the N-scaling problem  
when turning up more routers in a mesh, lowering CPU load because of  
less neighbors to interact with, and/or because their topology lends  
well to dividing things up for example.  40 routers in a mesh is not  
un-heard of.

David

On May 11, 2007, at 10:23 AM, Darrell Hyde wrote:

> The biggest constraint on the size of an IBGP mesh is memory. Let's  
> say
> you have 5 border routers each taking a full view from a different
> provider, and some core switches taking a full view from each border
> router - while your border routers will only need enough memory for a
> single view, the core switches in this case will need enough memory to
> hold all 5 views in their RIB.
>
> > -----Original Message-----
> > From: Rick Kunkel [mailto:kunkel@...]
> > Sent: Friday, May 04, 2007 2:31 PM
> > To: isp-bgp@isp-bgp.com
> > Subject: [isp-bgp] Size of iBGP Mesh
> >
> > Heya folks,
> >
> > I'd read somewhere recently that an iBGP mesh shouldn't
> > contain more than
> > a few routers.  I'm aware of route-reflectors, confederations, and
> > peer-groups to make things a little easier to manage.
> > However, I swear I
> > remember reading lately that there were negative issues with
> > these methods
> > (althuogh I can't remember what the issues WERE), and that there  
> > was a
> > better way to do things...  Is my memory shot?
> >
> > Thanks,
> >
> > Rick Kunkel



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