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Dial-up over AUX Port

I need help on AUX-Modem-Dialing configuration !

On my local side, I have Cisco 3640 with one PRI port, 30 mica modems configured. On the remote side, there is AS5300 device but the PRI interfaces are used for some other purposes. Just to manage that device from my central office, I tried to connect 3640 with the remote side over the AUX port of AS5300.

On AS5300, I have created Async interfaces and configured necassary (hopefully) items under the aux 0 interface. I did not use dialer interface commands. Modem call was initiated by central 3640 router. However, I was not succeeded in connection. Remote AS5300 successfully identifies the connected modem but there is nothing about connectivity. "Line is up, but line protocol is down" is the answer of "show int ser x/y" command on 3640.

Am I doing right things, or should I use dialer interfaces? What is the proper way of doing such a connection?

Any aid will be helpful. Thanks a lot,


  • Other Network Infrastructure Subjects

Re: Dial-up over AUX Port

If I understand correctly you want to have an exec session to the as5300 thru the modem on Aux port / dialing out of the 3640.

The easiest way to do so is by reverse telnetting into one of the mica modems on the 3640 & dialing using ATDT to the remote end. To reverse telnet into mica:

telnet (2000+line number corresponding to a modem)

say, telnet 2033, type AT, should get an OK


On the as5300, under the line aux 0 need the following:

modem inout

transport in all

flow hardware.

thanks, Mak.


Re: Dial-up over AUX Port

Since you don't share what you have configured, there is no way to tell what is keeping your configuration from working properly. While the AS5300 could be considered a unique beast and I have no personal experience with it, I have yet to run into an AUX port on a Cisco router which did not support dial backup. If you want a "second opinion" there is a white paper "Using the AUX Port on Cisco Routers for IP/IPX Router to Router Communications" on my web site which walks you through a working AUX to AUX routing example.

FWIW: The most common cause of problems is forgeting the "default routing" statement and using the wrong async interface number (for example, AUX0 is Async1 on a 25xx and Async65 on a 26xx. Make sure you use the right value for the 5300.

Good luck and have fun!

Vincent C Jones

Cisco Employee

Re: Dial-up over AUX Port

AUX port on a cisco router does support DDR so it does support dial backup as well. Here is the url for AUX-toAUX port async backup

Also there is a step by step config and troubleshooting help with debug on cco as well for dialout using AUX port. Pl. see