From: CCIE yong (ccie_yong@xxxxxxxxxxx)
Date: Thu Aug 30 2001 - 03:56:52 GMT-3
Hi, few doubts that have been inside my mind
1) backup - bri will be down when primary is up, when primary down, the bri
will be activated, must it be accomplished together with routing protocol,
os it can be done with static route/floating static.
2) when doing ipx isdn backup (the one like in bootcamp lab 8b)- mentioned
that use floating static to acomplish the task, and emphasize that ISDN
should never come up unless there is a failure on the Primary interface, but
if we configure floating-static, if the router with the floating static
initiate a ipx ping to an address that is not in the ipx routing table, it
will triggered the isdn line to dial since that is the last resort, if this
is the case, did we fulfill " ISDN should never come up unless there is a
failure on the Primary interface" ??
confuse...
3) to what I've read, the snapshot routing PRIMARILY is to prevent frequent
dialing of the isdn line by the routing update, not so much for the backup
purpose, either for IP or IPX, am I right ??
Appreciate your input,
Thanks in advance.
Yonger
>From: "Stanford M. Wong" <stanford@cns-hawaii.com>
>Reply-To: "Stanford M. Wong" <stanford@cns-hawaii.com>
>To: "Matt Wagner" <miguknom@hotmail.com>, <ccielab@groupstudy.com>
>Subject: RE: ISDN (Lab next week)
>Date: Wed, 29 Aug 2001 19:37:57 -1000
>
>here are some things that you can add to your list and others that are
>interested -
>
>Backup - you can either wait until the link fails but also when a threshold
>of traffic is exceeded on your primary link. Be careful when backing up a
>frame interface link though. Since back up will only monitor the physical
>status of the interface, if the other side of the FR link goes down the
>backup may never come up since the physical state of the line is still
>"up".
>In this case you would have to use a subinterface with the frame-relay
>interface-dlci command. that way when the other side of the frame relay
>link goes down, that DLCI will go inactive thus activating the backup
>interface (this is what I learned at my local cisco academy by the way).
>Keep in mind that the Frame Relay DLCI does take awhile to go inactive,
>then
>and only then with the backup interface timer kick in. I would suspect
>this
>type of issue would also exist for ATM too, but I haven't tested it.
>
>For distance vector routing protocols like (RIP v1, IPX RIP, IGRP) you can
>use the snapshot routing. Be careful on using it on a physical or dialer
>interface. It is a little different. You should practice to make it work
>both ways.
>
>For ospf you can use the ospf demand network keyword to keep the link down.
>
>There is also the watch list which works with the watch group. When a route
>is loss, the watch group can bring up the isdn link. This works with OSPF
>and EIGRP too.
>
>The good old fashion way to bring up a back up link is the good old static
>routes with a distance greater. I have seen people use this with the
>default and a route that they want to monitor. Of course you should know
>your distances for all the routing protocols so you can make this static
>route higher.
>
>Hope this helps you...and good luck with your lab attempt...don't forget to
>treat this as a positive experience....it was for me...three whole times...
>
>stanford
>
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
>Matt Wagner
>Sent: Wednesday, August 29, 2001 7:08 PM
>To: ccielab@groupstudy.com
>Subject: ISDN (Lab next week)
>
>
>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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