Configuring a Modem on the AUX Port?

Posted on 2007-10-03
Last Modified: 2016-08-29
Hello All -

I'm trying to configure a 1700 series router to allow dial up connections into the AUX port to allow inbound communications. My tech at the remote site installed the U.S. robotics 56k modem with a standard phone cable (RJ11) from the jack to the modem. We are using a Cisco rolled cable with a DB-25 connector from the modem to the AUX port on the router. I have configure the router per this Cisco article:

Needless to say I can't get it to work :\

I can post the config output if needed. Any ideas?
Question by:Marc_Johnson

    Author Comment

    I was just testing this and it looks like I'm stuck on number (4) in that Cisco document. I can telnet to the router using it's IP address the port and line number, but after it asks me to authenticate it says "OK" and doesn't allow me to type any more commands:

    telnet 2005

    Here is the portion of the article I'm stuck on:

    Use the reverse telnet method on the modem to configure the appropriate initialization string.

    For more information on reverse telnets, see Modem-Router Connection Guide or Establishing a Reverse Telnet Session to a Modem.

        maui-rtr-10#Telnet 2065

        !--- The IP address is the Ethernet address on the router.
        !--- 2065 represents 2000+line 65. Refer to the documents mentioned above,
        !--- if the reverse telnet fails.

        Trying, 2065 ... Open

        !--- Modem attention command.


        !--- The modem responds with an OK. If you receive any other message,
        !--- or no response at all, replace the modem hardware.
    LVL 79

    Accepted Solution

    The OK is coming from the modem and is exactly what you are supposed to see.
    Follow step #4 and type the init string


    If you are setting this up to dial into the router console for remote management, I would highly suggest connecting not to the AUX port, but rather to the CONSOLE port.
    You configure the modem separately as per the instructions in the link. This gives you the ability to dial into the router even if it is stuck at a rommon> prompt and cannot load the IOS.
    LVL 9

    Assisted Solution

    I used this document to configure modem access to my routers, via hyperterminal.
    Worked a treat, hyperteminal dials the number and you get the nabber and login prompt.
    I can post router config if you like.
    How are you initiating the connection ?

    Author Comment

    Thanks for the replies...

    Irmoore - Once I login using reverse telnet on the AUX port it asks me to authenticate, then it tells me my password is ok but once it gets to this point it will not let me type anything, it just sits there?

    Trinak96 - I will take a look at the that article as well.

    Also, although there are some good advantages (as well as disadvantages) of being able to configure the access through the console port, would rather just use the AUX port. These modems and phone lines are only being put into place for a short period of time as a backdoor during the FR to MPLS conversion.

    Can you think of any reason why I can't issue any of the modem commands after authentication?

    Here is the config for the AUX port:

    Washington_DC#sh line aux 0
       Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
    *    5 AUX 115200/115200- inout     -    -    -      7       0     0/0       -

    Line 5, Location: "", Type: "ANSI"
    Length: 42 lines, Width: 80 columns
    Baud rate (TX/RX) is 115200/115200, no parity, 2 stopbits, 8 databits
    Status: Ready, Connected, Active, No Exit Banner
    Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol Out
      Modem Callout, Modem RI is CD
    Modem state: Ready
    Modem hardware state: noCTS noDSR  DTR RTS
    Special Chars: Escape  Hold  Stop  Start  Disconnect  Activation
                    ^^x    none   -     -       none
    Timeouts:      Idle EXEC    Idle Session   Modem Answer  Session   Dispatch
                   00:10:00        never                        none     not set
                                Idle Session Disconnect Warning
                                Login-sequence User Response
                                Autoselect Initial Wait
                                  not set
    Modem type is unknown.
    Session limit is not set.
    Time since activation: 00:18:57
    Editing is enabled.
    History is enabled, history size is 10.
    DNS resolution in show commands is enabled
    Full user help is disabled
    Allowed transports are pad telnet rlogin.  Preferred is telnet.
    No output characters are padded
    No special data dispatching characters

    Author Comment

    I pulled up a telnet session to the router and then started another one using Reverse Telnet. When I issue the "show users" command I can see that I have connected to the AUX port see below:

    Washington_DC#sh us
        Line       User       Host(s)              Idle       Location
       5 aux 0                idle                 00:00:16 192.168.X.X
    *  6 vty 0                idle                 00:00:00 192.168.X.X
       7 vty 1                idle                 00:00:48 192.168.X.X

      Interface  User      Mode                     Idle Peer Address

    On the reverse telnet session that wont let me issue commands it hangs on this screen

    User Access Verification

    Password OK

    Once I issue the command "clear line 5" from the other session it kicks me out. I have connectivity but I can't issue any commands?
    LVL 79

    Expert Comment

    I promise that connecting to console port is easier to do, and will serve you better as remote access during a changover of services.
    Here's step by step guide that I have used hundreds of times without fail. The USR init string in the Cisco document above does not work properly:

    Here's another reference on reverse telnet to the modem:


    Author Comment

    The problem I'm having is that we have 3 modems.

    1 is connected in Chicago office
    1 is connected in the DC office
    1 is local to us here for Dialing into the above mentioned offices

    The modems are connected to the routers, Chicago in the AUX port and DC in the Console port.

    The last document I read assumes I have local access to these modems, but I don't.

    We don't have IT staff in these locations, only here at the main site.

    I have never configured a router for dial-in access, and up until now forgot about the AT commands :)

    I'm really stuck here, I can't dial into the routerrs and I can't gain access to issue any of the AT commands of the modems. I'm not sure what I'm doing wrong. I have followed the Cisco doc and attempted following the other one posted by Irmoore.

    Can I get this to work even though I'm not in these remote locations and cannot issue the AT commands on these modems? The router sees it but once I login to the router using rTelnet I can't issue any AT commands :\

    This is now critical so I'm raising the point value. I need to get these up this weekend!

    Thank you ~

    Author Comment

    Looks like these issues were with the routers themselves. Thanks for all your help on this one

    Expert Comment

    Marc, I am having the same issue as you.  Im prompted after the reverse telnet with a login prompt..and cant type anything after authenticating.

    what was your solution?

    Expert Comment

    Same issue; the problem with the routers was...???

    Featured Post

    How to run any project with ease

    Manage projects of all sizes how you want. Great for personal to-do lists, project milestones, team priorities and launch plans.
    - Combine task lists, docs, spreadsheets, and chat in one
    - View and edit from mobile/offline
    - Cut down on emails

    Join & Write a Comment

    I have seen some questions on problems with SSH/telnet access to Cisco routers that may occur despite the fact that from a PC connected to your LAN, Internet connectivity is in place and users can access Internet sites without any issues.  There are…
    I recently attended Cisco Live! in Las Vegas, a conference that boasted over 28,000 techies in attendance, and a week of hands-on learning hosted by a solid partner with which Concerto goes to market.  Every year, Cisco displays cutting-edge technol…
    After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
    After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

    734 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    20 Experts available now in Live!

    Get 1:1 Help Now