What a week, I’ve worked 70 hours so far… a lot of it on getting our modem dialback system to work!.

So I use a Cisco 2811 loaded with a WIC-1AM-V2 and a Async card also to provide remote console access to our devices, thus if all the wan circuits drop theres still another way in!

The problem I’ve had this week is that the modem just would not dial, it refused, the only error message I got was “Async 0/2/0 reset by async dial out failure” (or something along those lines). I suspected that the telco was either delaying the sending of dialtone or was sending a stuttered dialtone (e.g. with message waiting).

The best way to troubleshoot this is to telnet straight to the modem and issue AT commands to it to see if you can force a dial out. This will check the modems working ok:

Firstly you need to find out what line your modem is operating on, do a sh run | include 115200. This should only show the modems you have in the system. In this example I’m going to use line 50.

Next, telnet to the terminal server on line 50, e.g. telnet 192.168.0.249 2050. If you’ve put a password on your lines then you’ll need to enter it. You should then be left with nothing, to check you’ve sucsessfully connected to the modem type: AT, the modem should respond with OK.

Now attempt to dial out:

AT
Modem responds: OK
ATZ
Modem responds: OK
ATDT\T<00441494123321>

If there is a problem with the dialtone it will respond: NO DIALTONE

To try again, this time without waiting for a dial tone:
AT
Modem responds: OK
ATZ
Modem responds: OK
ATX3
Modem responds: OK
ATDT\T<00441494123321>

If you have connected successfully you’ll see:
CONNECT 115200/V92/LAPM/V44/28800:TX/46667:RX

Bingo! So now we need to tell the 2811 to do this every time to dial out. The way we can do this is with a chat script. Modemcap is a possibility but the “default chat script” will reset the modem after the modemcap has happened so we can’t use modemcap.

From global config mode:
(config)#chat-script nodialtone “” “ATZ” OK “ATX3″ OK “ATDT\T” TIMEOUT 60 CONNECT \c

(NOTE: We don’t need to put the phone number in there, Cisco will handle that!)

Then apply the chat-script to the modem line (in this case line 0/2/0):
(config)#line 0/2/0
(config-line)#script dialer nodialtone.

Now when you dial out using a dialer on that interface it will run that chat script. Problem solved!

To debug this lot use: debug modem, debug chat, debug async state, debug dialer.

Hopefully you won’t loose as much hair as me over this!