From: Christian Sica (csica@liweb.net)
Date: Thu Dec 29 2005 - 14:32:37 GMT-3
It is really important to understand how BGP is working here and understand
exactly how the route-reflector will fix your problem. As Brian mentioned
earlier, iBGP will not forward routes beyond its directly connected peers.
For example:
(R1)-----(R2)---(R3)---(R4)---(R5)
|AS100 | | AS200 |
Lets say R1 is advertising the route 10.0.0.0/8. It will forward this route
to it EBGP neighbor R2. R2 will then forward this EBGP route to its only
IBGP neighbor R3. That's as far as it will go. This is because BGP's loop
avoidance mechanism says that it will only forward routing information to
its directly connected IBGP neigbors. This happens when R2 forwards the
10.0.0.0/8 network to R3. However, since R4 and R5 are not neighbored up
with R2, neither of them will receive the 10.0.0.0/8 route. So in your
scenario you were able to get this route forwarded to R4 by configuring R3
as a route-reflector, thus making R4 its client. Lets say that the scenario
restricts us from adding additional IBGP neighbors to any router in AS200.
There are several ways we can solve this. Any thoughts?
Christian
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
CCIEin2006
Sent: Thursday, December 29, 2005 11:52 AM
To: Brian Dennis
Cc: Cisco certification
Subject: Re: Route Reflector Question
So even if R3 is not a client of R4, just the fact that R4 is a RR will
cause it to forward the IBGP update?
On 12/28/05, Brian Dennis <bdennis@internetworkexpert.com> wrote:
>
> To answer your own question, think about how BGP works:
>
> If you are a router in AS200 and you receive an iBGP update, would you
> forward that update onto another router in AS200 if you aren't
> configured as a RR?
>
> So now that we know R4 will not forward the iBGP update on we can
> solve this by configuring R4 as a RR or have R3 peer with R5 directly.
>
> HTH,
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
> bdennis@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> CCIEin2006
> Sent: Wednesday, December 28, 2005 3:07 PM
> To: Cisco certification
> Subject: Route Reflector Question
>
> Hello All,
>
> Could someone tell me how many times a route will be propagated in the
> following example:
>
> R1(AS100)--->R2(AS200)---->R3(AS200 RR)---->R4(AS200)---->R5(AS200)
>
> R1 is in AS100, all others are in AS200.
> R3 is configured as route reflector with R4 as the route reflector
> client.
>
> Basically I'm wondering if R4 will propagate the routes learned from
> R3 to R5?
>
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