From: Joseph Brunner (joe@affirmedsystems.com)
Date: Wed Nov 21 2007 - 15:38:45 ART
It's still a valid issue that must be solved in any lab or production
network.
How is it not relevant today?
Assume a network that does have/allow a default route
Assume one or more routers between bgp speakers are not running bgp
Assume BGP peering between those routers, across non-bgp speakers!!!
Now, guess what
A bgp speaker still should not advertise a prefix learned to peers unless
that prefix is in sync with the IGP.
Read Wendell Odom's CCIE exam cert guide. It's still just as valid an issue
as ever. I assume it's off by default because cisco assumes now that we run
bgp everywhere when this is often not the case.
Just because I inject something into bgp at the edge does not mean in the
core we will have a route to that destination once traffic is flowing in
towards those networks from external peers, etc.
I would say
-leave sync on and redistribute
-run bgp everywhere
Those are the safe choices.
-Joe
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Peter Van Oene
Sent: Wednesday, November 21, 2007 11:56 AM
To: Cisco certification
Subject: Re: synchronization ibgp amd igrp
I love that cisco tests on BGP synch ;-) what a useful feature that
is. I'm sure hiring managers are happy that CCIE's can be expected to
understand technology that hasn't been remotely relevant for well over
a decade. Here is a useful application of your time. SNA is way more
relevant.
P
On Nov 20, 2007 10:21 AM, Anthony Sequeira
<Anthony_Sequeira@skillsoft.com> wrote:
> First - make sure you completely understand the synchronization rule of
> BGP. This rule states...
>
> "A BGP router should not use or advertise to an external neighbor, a
> route that is learned from IBGP unless the route is local or the router
> learns it from an IGP."
>
> I always remembered this by thinking about BGP needing to be in
> synchronization with the underlying IGP.
>
> BGP synchronization is off by default in IOS release 12.2(8)T and later.
> Earlier releases had it turned on by default. I presume that it used to
> be on by default because for a long time it was fine to redistribute BGP
> routes into the underlying IGP and a full mesh of IBGP was not
> considered necessary.
>
> Once you FULLY understand the rule, it should not present any fears for
> you in the lab exam.
>
> For example, if they were to have you turn ON synchronization on the
> routers, and you are having trouble with prefix advertisement, then you
> would know where to look. Perhaps you were supposed to have the prefix
> in question advertised in an IGP somewhere!
>
> Anthony J. Sequeira
> #15626
> Recert Required? No Problem!
> http://www.netmasterclass.net/CCIE/Self-Paced-Program/Written
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> shady darwish
> Sent: Tuesday, November 20, 2007 9:39 AM
> To: Cisco certification
> Subject: sychronization ibgp amd igrp
>
> when do we have to use synch and why and when we don't
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Sat Dec 01 2007 - 06:37:30 ART