From: Randall Scheffer (Randall.Scheffer@xxxxxxxxxxxxxxxxxxxxxxxxxxx)
Date: Sat Jul 29 2000 - 22:28:21 GMT-3
Bill and Brian are both absolutely correct. I have spent days with two real
BRI lines testing this out. However, I would like to add a simple point
that had me running in circles.
If your dialer idle-timeout is set very low, say around approx 10-30 seconds
your link will flap. The best I can figure is while demand-circuit will
bring the link up to exchange new LSA's it is not considered interesting
traffic therefore will not keep the link up after the idle-timeout, KEEP IN
MIND THIS IS MY THEORY--NOT CISCO VERIFIED, therefore the link drops prior
to demand-circuit finishing so it starts over again...brings up the
link...link goes down before it's finished. Perhaps there comes a time when
it finishes however it will look broken until it does, if it does.
I like an idle-timeout of 150 to 300 seconds. Like most folks I had set my
idle-ti low to 15 seconds to speed up my troubleshooting...and it bit me.
Hope this helps,
Randall
p.s. If you have good reason to believe this is BS let me know, like I said
this is personal theory from personal troubleshooting.
-----Original Message-----
From: Bill Dicks [mailto:wdicks@structure-tech.com]
Sent: July 19, 2000 1:37 PM
To: ccielab@groupstudy.com
Subject: RE: How to configure OSPF over ISDN/DDR
Yes, one needs to carefully use distribute-lists for
redistribution...another things is to make the Loopback interface passive as
well, otherwise the rip traffic will get broadcast out the Loopback and come
right back in. That's what a loopback interface does, it loops traffic
back. So a RIP broadcast into Loopback 1 will come out Loopback 1 and if
RIP is redistributed into OSPF without a distribute-list, it will trigger
the line. Also, always use the "distribute-list 1 out rip" under ospf
rather than "distribute-list 1 in"...
Bill
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Brian S turner
Sent: Wednesday, July 19, 2000 1:07 PM
To: ccielab@groupstudy.com
Subject: RE: How to configure OSPF over ISDN/DDR
You cannot make the OSPF hello's uninteresting, because they must establish
the initial adjacency, and from time to time they have to update one another
on link state changes. If the routers are unable to send hellos to
eachother the adjacency will go down. Ip ospf demand suppresses the hellos,
but from time to time they still go. If you filter the hellos the protocol
is broken. Trust me I have tried it and also been told this by some
instructors trying to fix this same problem. The issue was explained
earlier. OSPF demand works fine until you load RIP/EIGRP/IGRP on the router
and assign a Major network, that encompasses the isdn link. Then what
happens is the interface goes down due to idle timer like its supposed to,
because you are suppressing hellos, and have passive interface in your
RIP/IGRP/EIGRP config. But the RIP/IGRP/EIGRP protocol is still being
redistributed into OSPF, so when they see that the ISDN is down, and it is
in the same major network as the one you have turned on for them, they send
out a flash update. Guess who gets the flash update? OSPF!! So, what has
now happened to OSPF? It has a linkstate change. According to the RFC it
has to update its neighbor of the linkstate change, so it brings the ISDN
link back up to pass on the info. Once the update is complete, the hellos
are still suppressed, so after your idle timer, the link goes down again,
and the cycle starts all over again.
Brian Turner
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Jeff Sapiro
Sent: Wednesday, July 19, 2000 10:15 AM
Cc: ccielab@groupstudy.com
Subject: Re: How to configure OSPF over ISDN/DDR
Another item I don't have the equipment to test - I never thought of
making OSPF uninteresting. How can this work? Doesn't there need to be
an initial exchange? It would certainly be an easy generic solution to
all those redistribution scenarios.
-Jeff
Brian Edwards wrote:
> Last time I answered this question I caused a huge raucus. So I'll try
> to be more politically correct this time.There may be some problems
> with OSPF demand circuit is some versions of IOS. The doc states that
> you should only have to configure demand circuit on one side of the
> connection. If this does not work for you try configuring it on both
> sides. If it still doesn't work make OSPF uninteresting in your
> dialer-list. After that upgrade to 12.0 and try all these steps again
> (1 side, both sides, OSPF uninteresting).In the CCIE lab you may not
> have the option of upgrading to 12.0, or you might not want to take
> the time. In this case, IMHO, make OSPF uninteresting (verifiy with
> the proctor if this is acceptable)./Brian
>
> -----Original Message-----
> From: Andy Singh [mailto:ansingh@cisco.com]
> Sent: Tuesday, July 18, 2000 9:31 AM
> To: ccielab@groupstudy.com
> Subject: How to configure OSPF over ISDN/DDR
>
> Hello Can any1 tell me how to configure OSPF over ISDN line
> so hello packets won't bring up the circuit. i think you can
> do "ip ospf demand circuit" inteface command but i can't get
> it to work like that. i'd appreciate any helpAndy
>
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