From: Theodore TZEVELEKIS (theodore_tzevelekis@xxxxxxxxx)
Date: Wed May 16 2001 - 21:59:58 GMT-3
I agree. With the virtual-link down, you have no intra-area route exchange.
However, R2 also belongs to area 2 so it can still exchange routes with R3.
One can imagine that we may be running some other protocol beyond R2-e3...
that's another story. The issue here is how will a default route get
installed in R2's table.
ospf demand-circuit is probably THE solution. I mean I don't see any way it
shouldn't work. I've done setups with OSPF-DDR before and they work fien
(except when combined to multiple dialer profies between two same peers used
as backups... but that's another story ;-) But! I don't want to run ospf
over the ISDN. That would mean extending area0 or area 2 over the ISDN.
Which does not fall within the specs that I have defined for myself ;-)
I just want to try to find a solution with this data. So far I haven't been
able to. And I'm beginning to lose hope :-(
The only workaround I found was to use my BGP to inject the route (yes I'm
running BGP over the whole thing as well) but
1. This is not a proper solution (I want to use my OSPF network to do it).
2. Last but not least: As soon as R2 gets a route from BGP, it will regerate
a default route back into R3, thus overriding the floating default pointing
to the ISDN and eclosing it into a loop (R2->R3 and R3->R2).
In this scenario, the only solution I found is to generate the default route
on R1, then just advertise it to R3 through R2 (thus not generate it locally
on R2). This way, when the link goes down, R2 loses its own default, gets
one from the BGP pointing to R3 and does not regerate one.
But as I said, this is a "dirty" solution. I don't like it.
Any comments?
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Roman Rodichev
Sent: Thursday, May 17, 2001 2:36 AM
To: ccielab@groupstudy.com
Subject: Re: Question: OSPF, DDR, backup routes
Very nice! I like it. But you can't do it.
As soon as R1-R2 connections is gone, Area 1 and Area 2 need some way of
connecting to area 0. You can only do it with a virtual link. But virtual
link will never run over the interface that is not running OSPF :)
try enabling ospf demand-circuit on the bri and tell us how it works out
>From: "Theodore TZEVELEKIS" <theodore_tzevelekis@yahoo.com>
>Reply-To: "Theodore TZEVELEKIS" <theodore_tzevelekis@yahoo.com>
>To: "ccie-groupstudy" <ccielab@groupstudy.com>
>Subject: Question: OSPF, DDR, backup routes
>Date: Thu, 17 May 2001 01:43:37 +0200
>
>Hi all,
>
>I've been trying to find a way to solve a very specific problem... wihtout
>any luck:
>
>You have 3 routers running OSPF:
>R1 (e0-area0, e1-area1, bri1 -> R3, virtual-link to R2)
>R2 (e0-area1, e1-area2(nssa), e3-area1, virtual-link to R1)
>R3 (e0-area2(nssa), BRI1 -> R1)
>
>OSPF is NOT running on ISDN.
>I inject a default route from R2 into area 3 therefore to R3, pointing to
>itself (R2) - default-information yada yada.
>
>Now what I want, is with just one default on R3, and statics on R1
>(floating
>in both occasions) to be able to access R2-e3 through the ISDN in the event
>of (R1-e1)<->(R2-e0) failure.
>
>What this means is that I have to somehow inject a default route into R2
>when the ISDN comes up (Reminder: in normal circumstabnce, R2 is injecting
>a
>default route into R3). Furthermore, OSPF does NOT redistribute static
>default routes. The only way I have found so far is to actually generate a
>default-info yada yada on R3 when the link comes up. BUT! as soon as R2
>receives this, it, in turn, generates a new default-info and injects it
>back
>into R3.
>
>Also, as the virtual link is down, I have to find a way to inject that
>route
>into the OSPF neighbors in area 1 hanging out of R2-e3.
>
>Any ideas?
>
>Thanks
>
>Theo
>
>
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