From: Robert Miller (rmiller@absitech.com)
Date: Thu Jan 16 2003 - 23:22:29 GMT-3
Circumstances will determine whether or not you would want to use this
method. In a real world situation, as stated in the book, if you are a stub
AS with a multihomed connection to an ISP, you may not want to redistribute
BGP into IGP because you don't want your routing tables being filled up by
potentially hundreds or thousands of routes. Doyle's example is one way to
prevent that.
However, if you're in the lab and its stated that you are not allowed to use
default or static routes, than regular rules of sychronization would
probably apply.
Later....Robert
-----Original Message-----
From: Peng Zheng [mailto:zpnist@yahoo.com]
Sent: Thursday, January 16, 2003 7:20 PM
To: Robert Miller
Cc: ccielab@groupstudy.com
Subject: RE: BGP synchronization
Is only a default route enough? When synchronization
is enabled, I think for each route to be inserted into
routing table, a same route should be learned from
IGP. Now only a default route is learned, I think if
a IBGP peer learns a default route, it will put it
into routing table. How about other routes?
Thanks for help.
--- Robert Miller <rmiller@absitech.com> wrote:
> 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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> > > > > .
> > > > >
> > > >
> > >
> >
>
This archive was generated by hypermail 2.1.4 : Sat Feb 01 2003 - 07:33:51 GMT-3