From: Robert Miller (rmiller@absitech.com)
Date: Thu Jan 16 2003 - 16:10:24 GMT-3
Follow the rules:
1. (pg 123) In order for IBGP to work, Peers must be fully meshed or routes must be redistributed into and syncronized with IGP.
2. If IBGP peers are fully meshed, syncronization must be disabled in order to inject routes learned from EBGP into the routing table as it traverses the IBGP group.
On pg 245, we know that sycronization was not disabled, so IBGP could NOT inject the routes into the routing table from the BGP table.
Based on LOCAL_PREF settings, both Zermatt and Moritz know from the BGP table which path they will take to the respective AS.
Now for the fun part!
1. We know that BGP did not inject the routes into the routing table because syncronization was not disabled.
2. We know that BGP is not redistibuted into IS-IS, so this did not inject the routes into the routing table.
3. But, Because default routes were created and injected into the routing table, the IBGP peers are able to get to their preferred paths.
Hope this helps....
Robert
------------------------------------------------
On Thu, 16 Jan 2003 07:53:03 -0800 (PST), Peng Zheng <zpnist@yahoo.com> wrote:
> I just took a look, but I didn't see the reason. It
> only mentioned it is different with the earlier
> examples. I don't know why synchronization is not
> disabled.
>
>
>
> --- Robert Miller <rmiller@absitech.com> wrote:
> > Peng,
> >
> > Look at page 245. It explains why the use of the
> > default route bypasses the affect caused by the IGP
> > (IS-IS) and synchronization.
> >
> > Later...
> >
> > Robert
> >
> >
> > ------------------------------------------------
> > On Thu, 16 Jan 2003 02:24:14 -0500, "cebuano"
> > <cebu2ccie@cox.net> wrote:
> >
> > > Peng,
> > > I haven't mocked up this lab yet, but based on the
> > configuration,
> > > Zermatt and Moritz are learning about AS50, 75 and
> > 100 via their eBGP
> > > peers as well so BGP synchronization should have
> > not effect on these
> > > routers' path selection. I'll let you know after
> > I've mocked this up.
> > >
> > > Gotta sign off now.
> > > Elmer
> > >
> > > -----Original Message-----
> > > From: Peng Zheng [mailto:zpnist@yahoo.com]
> > > Sent: Thursday, January 16, 2003 2:07 AM
> > > To: cebuano; ccielab@groupstudy.com
> > > Subject: RE: BGP synchronization
> > >
> > > I know the path is prefered. But because
> > > synchronization are not disabled on Zermatt and
> > > Moritz, the route learned only from IBGP should
> > not be
> > > put in routing table if it is not learned by IGP.
> > >
> > > Right?
> > >
> > >
> > >
> > > --- cebuano <cebu2ccie@cox.net> wrote:
> > > > Peng,
> > > > Check the LOCAL_PREF values for both iBGP
> > routers.
> > > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com
> > > > [mailto:nobody@groupstudy.com] On Behalf Of
> > > > Peng Zheng
> > > > Sent: Wednesday, January 15, 2003 11:56 PM
> > > > To: ccielab@groupstudy.com
> > > > Subject: BGP synchronization
> > > >
> > > > Hi,
> > > >
> > > > On page 242-244 of Routing TCPIP V2, why Zermatt
> > use
> > > > Moritz to 172.18.0.0?
> > > >
> > > > I think it's not synchronized because it's not
> > > > learned
> > > > by IGP.
> > > >
> > > > Any idea?
> > > >
> > > > Thanks for help.
> > > >
> > > > Best Wishes,
> > > > Peng Zheng
> > > >
> > > >
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