[nsp] ospf default routes and bgp injection

[Nick Kraal]

Steve,

Thanks for your reply. Redistributing BGP into an IGP and vice-versa are
known no-nos and an IGP should be used to carry only infrastructure
networks. Over espresso based arguments with other service providers here,
was wondering more along the lines of this. For a PoP for example, is there
any difference running aggregation via something like OSPF summary commands
in comparison to announcing aggregated prefixes via iBGP.

Regards,

-nick/

----- Original Message ----- 
From: "Steve Lim" <limmer at execpc.com>
Cc: <cisco-nsp at puck.nether.net>
Sent: Tuesday, April 06, 2004 9:37 PM
Subject: Re: [nsp] ospf default routes and bgp injection


> Here's an easy reference (text fishing at Cisco.com is annoying):
>
> Book: CCNP Self Study: BSCI by Paquet, Chp 8Advertising Networks into
> BGP, page 511-513.
>
> The segment referenced above simply declares that it's a bad idea. But
> the paragraph doesn't give exampls.
>
> Redistributing IGP into BGP has bad repercussions specifically if your
> IGP carries non-aggregated routes. The problem becomes acute when your
> link-state protocol detects flapping links. This causes the IGP to
> recalculate SPF (or appropriate algorithm) and announce this into BGP.
> BGP in turn adhusts it's tables. For Service Provider type networks,
> 5-10 flapping links can occur at any one time. Each subsequent flapping
> link causes an exponential (not incremental) change in IGP and BGP
> response. A prolonged non-converged network results in routing loops.
>
> Hope my simplified explanation helps.
>
> Nick Kraal wrote:
>
> > Following up on this one. We all know that the IGP of choice used should
> > carry only infrastructure networks and kept as small as possible. The
rest
> > should be announced via iBGP. Is there a document that explains this
> > rationale clear --having some difficulty convincing some folks.
> >
> > Thanks in advance,
> >
> > -nick/
> >
> > ----- Original Message ----- 
> > From: "Gert Doering" <gert at greenie.muc.de>
> > To: "Christopher J. Wolff" <chris at bblabs.com>
> > Cc: <cisco-nsp at puck.nether.net>
> > Sent: Thursday, April 01, 2004 5:49 AM
> > Subject: Re: [nsp] ospf default routes and bgp injection
> >
> >
> >
> >>Hi,
> >>
> >>On Wed, Mar 31, 2004 at 09:58:12AM -0700, Christopher J. Wolff wrote:
> >>
> >>>I've considered ibgp as an end-to-end solution however never went so
far
> >
> > as
> >
> >>>to implement it.
> >>
> >>Completely overkill in this network.  If there's no BGP speaker "down
the
> >>road", there is not much use in having all those routers actually carry
> >>BGP information.
> >>
> >>
> >>>My concern is making sure that the entire routing table
> >>>isn't propagated all the way to the edge device, which could be
> >
> > something
> >
> >>>minimal like a 2611XM.  Any thoughts?  Thank you for your advice.
> >>
> >>Have the BGP speakers distribute an OSPF (or EIGRP, or even RIP :) )
> >>default route to the smaller boxes.
> >>
> >>gert
> >>-- 
> >>USENET is *not* the non-clickable part of WWW!
> >>
> >
> > //www.muc.de/~gert/
> >
> >>Gert Doering - Munich, Germany
> >
> > gert at greenie.muc.de
> >
> >>fax: +49-89-35655025
> >
> > gert at net.informatik.tu-muenchen.de
> >
> >>_______________________________________________
> >>cisco-nsp mailing list  cisco-nsp at puck.nether.net
> >>https://puck.nether.net/mailman/listinfo/cisco-nsp
> >>archive at http://puck.nether.net/pipermail/cisco-nsp/
> >>
> >
> >
> > _______________________________________________
> > cisco-nsp mailing list  cisco-nsp at puck.nether.net
> > https://puck.nether.net/mailman/listinfo/cisco-nsp
> > archive at http://puck.nether.net/pipermail/cisco-nsp/
> >
> >
>
> -- 
> <><><><><><><><><><><><><><><><><><><><>
> Steve Lim - Network Engineer (Michigan)
> Corecomm -An ATX Communications Company
> How does a fool and his money get together?
>
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/