Strange problem with dialer persistent on multiple dialer interfaces -

Unanswered Question

I've come across some strange router behaviour to do with dialer persistant...

One of our customers requires the following solution:-

A router supporting a standard ADSL connection, but with an audio modem backup - so that connectivity can be maintained via an analog dialup if ADSL fails.

The hardware setup is an 837, running the latest available IOS 12.4(13b), with a USR robotics modem sharing the ADSL line (via a splitter) and plugged into the router console port.

The configuration uses dialer persistant on two interfaces and relies on "backup interface" to switch the backup connection on & off.

The problem.

a) Starting from ADSL up - all fine - can ping outside world.

b) Pull ADSL cable from router - audio modem dials out to ISP & reconnects - all fine.

c) Reconnect ADSL cable to router - audio modem disconnects - ADSL reconnects - all fine.

d) Pull ADSL cable from router 2nd time - audio modem **FAILS** to dial out -

connection stays down permanently.

This is totally repeatable upon router reboot.

Shut/no shut backup interface - no effect

Power cycle audio modem - no effect



Interface Dialer2,

no persistant dialer,

persistant dialer

--> **fixes** problem temporarily ??? (At least for one DSL failure cycle)

Is this an IOS issue - or am I missing something here ?

The fact that toggling the persistant dialer command on/off fixes the problem - does suggest to me that the issue does not lie with the audio modem.

Thanks in advance,


Please find attached config & debug dialer events for more detail.

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ohassairi Sat, 06/16/2007 - 21:50
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i can't answer your question but why you don't use 2 default routes with different metrics:

ip route Dialer1

ip route Dialer2 50

anharring Sat, 06/16/2007 - 23:50
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Is the Modem still busy from the previous call? - time out 120 seconds?

Does the ISP check for multiple MAC addresses on the same line - as you said you use the same line with a splitter?

Probably need to know what the Modem is doing:

#show modem summary

#debug dialer packets

#debug dialer events

#debug chat

#debug modem

PPP debugs, even though your not getting as far as PPP negotiation.

#debug ppp negotiation

#debug ppp authentication

#debug PPP events

Modem support and chat scripts:

Configuring and Troubleshooting modems:


I turned on the additional debugs, as requested - please see attached file.

(Its from a different router with identical hardware/slightly different IP - but behaviour is identical)

>Does the ISP check for multiple MAC addresses on the same line - as you said you use the same line with a splitter?

I'm running PPPoATM, so no mac addresses are involved here.

Looking at the debug, the async interface is never invoked 2nd time around.

Just want to do a sanity check here before I raise a TAC case.





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