From: Matt Wagner (miguknom@xxxxxxxxxxx)
Date: Thu Aug 30 2001 - 02:07:31 GMT-3
Hey folks,
I have my lab next week, and I am nervous about ISDN backup. I can
configure ISDN and troubleshoot it confidently, but in studying the docs and
the archives to find out the various ways to do DDR, I have managed to
confuse myself. What I am trying to clarify for myself (and anyone else who
needs it) is what the various methods of implementing a backup solution are
and what the basic componenets (not configuration details) of each are.
Here is what I am pretty sure of, and if anyone adds to it or corrects me I
will be grateful.
1. Backup interface. Simple enough-- the interface comes up as soon as the
primary link goes down and then the routers exchange routes. Not instant
failover, but easy to configure.
2. No backup interface/Dialer list config. This would require configuring
a dialer list that denies the routing protocol updates and permits other
sruff (IP, IPX, etc.). Obviously the primary link must be preferred over
the ISDN link. Should this then NOT flap? The problem with this is that
the local router won't know about remote routes via the ISDN link, so I dial
will never occur. I guess that I would then need snapshot routing, but if
so, what is the purpose of the dialer list denying the routing protocol in
the first place?
3. Snapshot routing. See #2 above.
I am making assumptions, of course, like "the ISDN link can't come up (flap)
until the primary link fails", etc. I know that this sounds kind of basic,
and I apologize for it being so, but although I can configure the various
pieces, I'm not clear on what constitutes a legitimate solution. It all
seems to overlap when I read up on it, and now I'm frazzled with a week to
go.
If it comes down to it, I don't mind giving up a couple of ISDN points; it
hurt me pretty badly timewise on my first attempt. But if anyone has a
concise summary or explanation to tie it all together, that would rock.
BTW, congrats on the recent CCIEs gt 8000. Your stories are inspiring, and
I hope to add my story to the archives Monday after next. We'll see...
Matt
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