From: yu chunyan (yuchunyan@hotmail.com)
Date: Tue Aug 05 2003 - 19:24:48 GMT-3
Hi,
In non-broadcast case, R3 believe it can reach R1 via frame relay, which
doesnot work unless you creat a frame relay in R3 mapping R1 address to the
dlci toward R2. If you forget it, R3 will have route to R1 in routing
table,but the next hop is not reachable. The point here is that routing
protocols treat frame relay as a broadcast media and doesnot change the
next-hop for routes.
Bin
>From: Jay Hennigan <jay@west.net>
>Reply-To: Jay Hennigan <jay@west.net>
>To: ccie2be <ccie2be@nyc.rr.com>
>CC: Group Study <ccielab@groupstudy.com>
>Subject: Re: IBGP neighbors over F/R
>Date: Tue, 5 Aug 2003 11:56:08 -0700 (PDT)
>
>On Tue, 5 Aug 2003, ccie2be wrote:
>
> > Hi,
> >
> > BGP wouldn't form peers between 2 spokes on a F/R hub and spoke
>topology.
> >
> > Here are the details:
> >
> > R3---------R2----------R1
> > spoke hub spoke
> >
> >
> > All routers are running OSPF and the F/R is in subnet 172.16.100.0/24
>and the
> > f/r interfaces were all left at their default ospf network types -
> > non-broadcast. The neighbor command was configured on R2 to allow it to
>form
> > ospf adjacencies with R1 and R3. R1 can ping R2 but not R3 and R3 can
>ping R2
> > but not R1.
> >
> > R1's loopback interface = 192.168.1.1 and R2's loopback = 192.168.2.2
>and R3's
> > loopback = 192.168.3.3
> >
> > The route table of each router shows all 3 loopbacks.
>
>Can you ping and/or telnet to the appropriate loopback from each of the
>neighbor routers?
>
> > R1 and R3 can both peer with R2 but they don't peer with each other. I
> > thought that as long as there was a TCP path ( the ip addr was in the
>route
> > table), R3 and R1 could peer. But this isn't working. Can someone
>explain
> > why not?
>
>Generally true. "In the route table" != "There is a TCP path", however.
>
>Policy routing, ACLs, and a plethora of other things can result in an
>address being in the route table yet unreachable. Don't despair. You
>now have a great opportunity to practice your skill with detailed show
>and debug commands!
>
>--
>Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net
>WestNet: Connecting you to the planet. 805 884-6323 WB6RDV
>NetLojix Communications, Inc. - http://www.netlojix.com/
>
>
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