ISDN Backup link Problem

Unanswered Question
Nov 4th, 2008

Hi,

I am having a problem with an ISDN back up link between a cisco 1841 (1841 Software (C1841-ADVIPSERVICESK9-M), Version 12.4(10)) and a cisco 3745 ((C3745-ADVIPSERVICESK9-M), Version 12.4(12)).

The description of the issue is that when the main link is taken down and the back up link comes up, as soon as the second channel on the BRI comes up the link drops.

I have found that the issue is caused becasue both sides of the link dial each other and cannot negotiate the line correctly. The workaround is to only have the dial string on one side.

This does pose a problem as if the main link goes down it can only be brought up by one side.

I have tried configuring dialer max-call 2 on the remote end and the dialer string on both sides but I get the same issue.

Does anyone know a resolution to this? I have pasted the config for both routers below.

Thanks,

####Remote Side####

interface Dialer1

ip address 172.30.157.2 255.255.255.0

ip accounting output-packets

encapsulation ppp

load-interval 30

dialer pool 1

dialer remote-name xxxx

dialer idle-timeout 14400

dialer string xxxx

dialer load-threshold 1 either

dialer-group 1

ppp authentication chap

ppp authorization ISDN

ppp multilink

####Local Side (3745) ####

interface Dialer2

ip address 172.30.157.1 255.255.255.0

ip accounting output-packets

encapsulation ppp

load-interval 30

dialer pool 1

dialer remote-name yyyy

dialer idle-timeout 3600

dialer-group 1

ppp authentication chap

ppp authorization ISDN

ppp multilink

I have this problem too.
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ohassairi Tue, 11/04/2008 - 23:27

if you are using "backup interface" under the primary interface, then there is a command called: backup delay.

To define how much time should elapse before a secondary line status changes after a primary line status has changed, use the backup delay command in interface configuration mode.

just make it different in both routers.

if you are using dynamic routing, then look at the timers of your dynamic protocol, may be if you change one of them (hold down for example) in one site, may be this will delay route insertion in routing table...

tcordier Wed, 11/05/2008 - 01:50

You could also use dialer-watch to trigger your ISDN backup on the remote side. By "watching" e.g. routes advertized from the local side, you can trigger the ISDN link at the remote side also for failures of the local side link, and it would obsolete the need to have a configuration which allows both sides to be able to dial out.

HTH, Thomas

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