From: Peter Van Oene (petvan@gmail.com)
Date: Wed Nov 21 2007 - 23:25:45 ART
> How is it not relevant today?
BGP to IGP distribution stopped scaling/being safe many years ago.
Indeed, its most SP's worst nightmare. Nothing like 200k routes
trying to synchronize across a distributed database.
> Assume a network that does have/allow a default route
Why? defaults are one of the most effective scaling tools one can employ.
> Assume one or more routers between bgp speakers are not running bgp
This is icky.. it pains me to assume it.
> Assume BGP peering between those routers, across non-bgp speakers!!!
Assume you hire someone to fix this silly network ;-) Exactly how
many routes will you put into your IGP? Is there some reason you'd
rather they be in the
IGP than BGP? Do you actually have a router that would be pleased
with a few thousand routes and a reasonable IGP but doesn't run BGP?
Don't mean to be overly facetious, but this methodology hasn't been
practical, nor espoused hopefully by anyone with a modicum of clue for
well over 10 years. I'm not even sure the code entirely works as it
was initially intended, and certainly no one is designing
functionality with synch in mind.
The reason I point it out, is I feel for you guys. It seems to me
that over time, the test gets less and less practical, and more and
more nit picky. This trend isn't good for anyone, let alone the
people devoting major time to get through it.
> 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.
Hold on here. BGP synch is designed for networks offering transit.
Networks offering transit run BGP, and do not stick OSFP only boxes in
the middle. Cisco is very safe in their assumption. I'm surprised
the feature is even still in IOS however know how hard it is to take
stuff out.
> 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'm not sure you understand what synch is for. Its not for routes you
inject yourself, rather routes you learn from peers, and expect to
provide transit across your core to other peers for.
> I would say
>
> -leave sync on and redistribute
> -run bgp everywhere
>
> Those are the safe choices.
Well, lets just say I agree with one of those.
I think synch is my pet peeve.. i'm always sticking my head into these
threads ;-)
> -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
> >
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