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Re: iBGP RR Cluster ID - What is best practice? posted 11/25/2008
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Huan,

Bunch of us had a good discussion regarding RRs and cluster ids, do a search
and i am sure you will find it beneficial.

On Mon, Nov 24, 2008 at 8:15 PM, Huan Pham
<Huan.Pham@xxxxxxxxxxxxxxxxxxxx>wrote:

> Hi GS,
>
> Doc CD and mosts other sources state that Cluster is use to prevent
> routing loop within an AS, when RR Client peers with more than one Route
> Reflectors. I do not see this point!
>
> I do accept that, there might be duplicate updates, resulting in
> inefficient use of bandwidth and CPU, as clients potentially will
> receive the same prefix from more than one Router Reflectors (RR).
> Clients then might advertize the route received by one RR to other RR.
> However, I cann't see where the routing loop can take place, given the
> fact that within an iBGP cloud, the next hop for a prefix does not
> change.
>
> One the other hand, if we set up two Router Reflectors with the same
> Cluster ID, we might remove redundancy in some cases.
>
> Here's an example. Normally R1 peer with both RR1 and RR2. But if
> there's a network problem, and peering between R1 & RR2  as well as RR1
> & R2 are lost. The iBGP peering topology in this case is:
>
>        (RR1)      (RR2)
> R1 ----- R4 ------- R5 ------R2
>
>
> In this case, RR1 sends update for any R1 networks to RR2, but RR2 will
> reject it, because of the same Cluster ID. As a result of this
> behaviour, both RR2 and R2 will lost connectivity to R1 subnets.
>
> Similarly, both R1 and RR1 will lost connectivity to R2 subnets.
>
> Here's a sample debug outputs.
>
> RR1#debug ip bgp updates
> BGP updates debugging is on for address family: IPv4 Unicast
> *Mar  1 00:26:59.347: BGP: 45.0.0.5 RR in same cluster. Reflected update
> dropped
> *Mar  1 00:26:59.351: BGP(0): 45.0.0.5 rcv UPDATE w/ attr: nexthop
> 25.0.0.2, origin i, localpref 100, metric 0, originator 25.0.0.2,
> clusterlist 0.0.0.45, path , community , extended community
> *Mar  1 00:26:59.359: BGP(0): 45.0.0.5 rcv UPDATE about 22.22.22.0/24 --
> DENIED due to: reflected from the same cluster;
>
>
> My question is,  what is the "best practice" with Route-Reflector ID.
> Should we set it? Or leave it off totally??
>
> Cheers,
>
> Huan
>
>
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-- 
Narbik Kocharians
CCSI#30832, CCIE# 12410 (R&S, SP, Security)
www.MicronicsTraining
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Sr. Technical Instructor