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RE : Lab6 Cisco r&s Prac Labs ISDN wording posted 09/08/2004
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Hi John, the problem with using the backup command is you are breaking the
requirement "...R3 and R5 should be able to ping each other..."

After reading his explanation I have come to the conclusion that it is not
really a backup solution the author is asking for, nor is there a
requirement for it. We can see in the breakdown solution that ISIS only goes
through the isdn line once he pings through the bri interfaces so he is
effectively fulfilling all his requirements.


-----Message d'origine-----
De : john matijevic [mailto:matijevi@xxxxxxxxxxxxx]
Envoyi : Wednesday, September 08, 2004 6:00 PM
@ : 'James'; ccielab@xxxxxxxxxxxxxx
Objet : RE: Lab6 Cisco r&s Prac Labs ISDN wording

Hello James,
Yes this is an error in the book, please visit my forum, as there are
many errors already pointed out there, already. Backup interface is the
solution I used as well.


John Matijevic, CCIE #13254, MCSE, CNE, CCEA
IgorTek Inc.
151 Crandon Blvd. #402
Key Biscayne, FL 33149
Hablo Espanol

-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of
Sent: Wednesday, September 08, 2004 3:23 AM
To: ccielab@xxxxxxxxxxxxxx
Subject: Lab6 Cisco r&s Prac Labs ISDN wording

In Lab 6 on practice labs , under ISDN, we see the following:

"Make sure that yourrouting proto is passed accross the isdn link only
the connectivity is established"

In order to accomplish the above, we simply make sure 'dialer-list 1
clns permit', and ensure that "clns_is" is not included -- thereby
ISIS establish adjacency only when ISDN circuit is already up and
So far so good. (well also ensuring dialer map clns yadda yadda..)

"The ISDN link should only pass a routing protocol if R5-fa0/0 is down."

Now.. it says ISDN should pass routing protocol when fa0/0 on R5 is
That is good and all when FA0/0 sudden goes down while ISDN is already
and running. But what happens when ISDN is NOT dialed and turned off
(due to
idle traffic)?? The previous requirement says that isdn must only
ISIS protocol when the circuit is already dialed and running.

So the thought process here in my head is to use 'backup interface' on
or another mechanism that will trigger ISDN to dial itself during fa0/0
This will ensure ISIS will establish adjacency then, after fa0/0 outage,
since backup interface brought up the ISDN circuit physically.

But the solution in the book made no configuration changes for this

Well, not making any config changes for this requirement works well when
isdn is already dialed and up and running, but guarantees nothing when
reboots your routers and isdn is shut down at boot time :(

Any ideas, clues?

James Jun                                            TowardEX
Technologies, Inc.
Technical Lead                        Network Design, Consulting, IT
james@xxxxxxxxxxxx                  Boston-based Colocation & Bandwidth
cell: 1(978)-394-2867           web: , noc:

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