From: Russell Lusignan (rlusignan@xxxxxxxxxxxxxxx)
Date: Thu May 03 2001 - 17:06:42 GMT-3
When synchronization is turned on on RouterA, and RouterA router receives a
route from an IBGP peer (RouterB), that route must already exist in
RouterA's routing table learned from an IGP before it will advertise that
route to any EBGP peers. Synchronization will ensure that routerA won't
advertise a route to an EBGP peer that it cannot route traffic to itself.
-Russ
> -----Original Message-----
> From: mcaplan.cs@clearstream.com [mailto:mcaplan.cs@clearstream.com]
> Sent: Thursday, May 03, 2001 1:39 PM
> To: ccielab@groupstudy.com
> Subject: BGP and no-sync
>
>
> Hi,
>
> I have a question regarding the effects of no-sync on BGP.
>
> The rule for synch, as far as I know is that an IBGP peer
> will not advertise
> a BGP route to another peer (IBGP or EBGP) if that route does
> not exist in
> the IGP.
>
> From my observations, a corollary to that is that a BGP peer will not
> install learnt BGP routes into the routing table if sync is turned on
> (assuming no redistribution). This is shown by comparing 'sh
> ip bgp' with
> 'sh ip route'; if sync is on, then routes will be visible in
> the BGP routing
> table, but will not be in the IP routing table. To get these
> BGP routes into
> the IP routing table, one has to simply do a 'no sync'.
>
> I'm just thinking aloud here, but I would appreciate some
> confirmation of my
> logic.
>
> Thanks
>
> Mark
>
>
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