From: Erick B. (erickbe@xxxxxxxxx)
Date: Sat Jan 20 2001 - 17:31:29 GMT-3
Shaun and others,
Thanks for the replies. I have figured out the problem
we were having. I've been focusing on other study
topics lately and was helping a friend out when he was
studying OSPF and ran into problems that I didn't run
into. Good experience and good to see. The problem was
on the other router without the backup interface. OSPF
was interesting traffic and this router kept trying to
dial in to the standby circuit but was getting
rejected. Added deny ospf any any to dialer-list ACL
and it cleared up the problem.
It's always good to work with others as you may not
create a problem and they might. Nice way to
troubleshoot and learn about the workings in more
detail.
As for IP ospf demand-ciruit for backup... in my
experience it's not a backup method. It doesn't
prevent a dial line from coming up/going down. It just
prevents hellos and flags routes as DNA. What I'm
trying to say is if you have a dialer interface
configured for OSPF and the dialer-list is wide open
and the other end is in standby mode (or can't answer)
then OSPF traffic will trigger a call *unless* a OSPF
relationship was formed previously and the OSPF
database has existing routes marked as DNA (scenario 1
below).
I saw the 2 results from my lab tests:
1) If a OSPF neighbor adj was formed over dialer
circuit the routes will be learned and marked as DNA.
No hellos since this is a demand circuit. Now the
dialer interface goes down, both routers have these
routes in their database and aren't sending hellos so
the dialer interfaces aren't being triggered by OSPF
traffic with a wide-open dialer list.
2) If a lower cost OSPF route between these routers
comes up then those become active. In the OSPF
database, the dialer/DNA routes are cleared and the
new lower cost routes are put in the database. With a
wide-open dialer-list OSPF traffic triggers the dialer
interface.
Thanks everyone for their comments.
Erick
--- Shaun Nicholson <Shaun.Nicholson@kp.org> wrote:
> Ok
> If I were setting this up I would set up 2 dialer
> interfaces one for the backup circuit and one
> running the demand circuit.
>
> I have never tried running them both on the same
> interface but as the dialer goes into standby I
> would imagine that the circuit was unusable until
> the serial fails but like I say I've never tried it.
>
> I would have to ask why do you need the backup
> command anyway, OSPF demand circuit dialer is a
> solution on its own. The backup interface command
> only puts the interface into active mode when the
> serial line fails so you still need traffic to bring
> the circuit up. I would certainly not block all OSPF
> traffic from making the link active because of this
> reason.
>
> If your interface ever bounces using the ospf demand
> circuit make sure all other IP routing protocols on
> that router have a passive interface for the BRI.
> Check what LSA's are bringing the line by debugging
> LSA generation and if thats still no good use the no
> peer neighbor-route command that always seems to
> work for me but you need to check the LSA generation
> first.
>
> I would just use the OSPF demand circuit and forget
> about the backup interface you dont need it and if I
> got a similar situation in the lab I would still
> take that approach and then justify why I did it
> that way to the proctor. If I was specificly told I
> had to use the backup interface and was not allowed
> to put OSPF on the bri interface then I would look
> at the backup interface as the solution.
> If I was told I HAD TO use both then I would set up
> 2 dialer interfaces. One for backup and one running
> OSPF demand.
>
> But again I dont see how you could use ospf demand
> circuit with the backup the interface goes int
> standby so becomes unusable until the interface your
> backing up fails. So why use demand circuit do you
> see what I'm saying??? I have been wrong and will
> probably be wrong again so please if this does work
> I'm sure someone will let me know.
>
> One or the other in my opinion.
> So check the wording on the lab if this was to
> appear and if you have to use OSPF on the bri then
> OSPF demand is IMHO the only solution.
>
> Thanks
> Shaun Nicholson CCIE 6705
> Lead Network Engineer
> Kaiser Permanente
> Silver Spring Data Center
> 301 680 1462
>
>
>
>
> erickbe@yahoo.com on 01/18/2001 10:27:00 PM
> To: ccielab@groupstudy.com@Internet
> cc: (bcc: Shaun Nicholson/MD/KAIPERM)
> Subject: OSPF Demand circuit on backup interface
>
> Hello,
>
> I have a question regarding using ospf demand
> circuit
> on a ISDN dialer interface that is in standby mode.
> Main serial interface has backup interface command.
>
> The problem is that with the ip ospf demand circuit
> command on the dialer interface the dialer interface
> keeps going up and down when the primary circuit is
> up
> and active. It is in standby mode when it does this.
> With the ip ospf demand circuit command off the
> dialer
> interface it stops going up & down and behaves like
> a
> standby circuit should.
>
> I have tried deny'ing OSPF in the dialer list,
> moving
> the ip ospf demand circuit command to the remote end
> router and it continues to go up & down while in
> standby mode. Anyone have any ideas?
>
>
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