In many situations, it would be necessary to allow a router to accept
interactive command processor of Cisco IOS (EXEC) calls with a modem connected
to the auxiliary (AUX) port of the router. This document provides the necessary
configuration tasks to configure such a scenario.
Note: This document does not cover a Point-to-Point Protocol (PPP)-based
connection that uses the modem on the AUX port. For more information on a
PPP-based connection, see
Dialout using a Modem on the AUX Port.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware
For more information on document conventions, see the
Technical Tips Conventions.
This document uses the network setup shown in figure 1.
Figure 1 – Network Diagram
To configure a modem on the AUX Port for EXEC dialin connectivity,
complete these steps:
Connect the cable from the AUX port of the router to the modem, as
shown in figure 2.
Remember these points:
Figure 2 – Connect the Cable
The AUX port on Cisco routers is either RJ-45 or DB-25. If the
AUX port is RJ-45, use a flat-satin rolled RJ-45--RJ-45 cable (part number
CAB-500RJ= ), which is usually provided with every Cisco router for console
connections. You also need an RJ-45 to DB-25 adapter marked "MODEM" (part
number CAB-25AS-MMOD) to connect the rolled cable to the DB-25 port on the
If your router has a DB-25 AUX port, use a straight-through
DB-25Female - DB25Male RS-232 cable to connect the modem to the router.
For more information on cabling, see
Connection Guide and
Guide for RJ-45 Console and AUX Ports.
Use the show line command to determine
the async interface of the AUX port.
Though most routers have the AUX port as line 1, access servers
have the AUX port interface after the TTY lines. For example, if your router
has 16 async/modem lines, the implication is that the AUX port is line 17.
Configure the AUX port based on the outputs of the show
line command. Here is an example to verify that the AUX port
configuration is on interface line 65:
Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
* 0 CTY - - - - - 0 0 0/0 -
65 AUX 9600/9600 - - - - - 0 1 0/0 -
66 VTY - - - - - 0 0 0/0 -
67 VTY - - - - - 0 0 0/0 -
68 VTY - - - - - 0 0 0/0 -
69 VTY - - - - - 0 0 0/0 -
70 VTY - - - - - 0 0 0/0 -
Line(s) not in async mode -or- with no hardware support
Use the following commands to configure the router AUX
We have previously verified that the AUX port is on line 65:
!--- Permit incoming and outgoing calls on this modem.
!--- Line speed to be used to communicate with the modem.
!--- Verify that the AUX port supports this speed.
!--- Refer to Bitrate Information for supporting information.
maui-rtr-10(config-line)#transport input all
!--- Allow all protocols to use the line.
!--- Enable RTS/CTS flow control.
!--- Use the password configured on the line to authenticate
!--- incoming connections.
!--- This password is configured below:
!--- The router uses this password (cisco) to authenticate incoming calls.
!--- For security purposes, replace "cisco" with a secure password.
Optional Configuration: If the router does not
have an enable secret password, incoming connections will not
be able to enter the enable mode. To allow incoming calls to enter enable mode,
use the enable secret
command to setup the
enable secret password.
Use the reverse telnet method on the modem to configure the
appropriate initialization string.
For more information on reverse telnets, see
Connection Guide or
a Reverse Telnet Session to a Modem.
maui-rtr-10#Telnet 172.22.53.145 2065
!--- The IP address 172.22.53.145 is the Ethernet address on the router.
!--- 2065 represents 2000+line 65. Refer to the documents mentioned above,
!--- if the reverse telnet fails.
Trying 172.22.53.145, 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.
!--- At followed by the initialization (init) string for this modem.
!--- The init string for this US Robotics modem is &f1s0=1.
!--- Note: USR modems must also have dip switch 3 and 8 down (DOWN = ON).
!--- Dip switch 3 = ON for Result Code Display.
!--- Dip switch 8 = ON for AT Command Set Recognition.
!--- If you use another modem brand, refer to the Modem-Router
!--- Connection Guide for your manufacturer-specific modem init strings.
!--- The modem responds with an OK. This means that the modem was
!--- successfully initialized.
!--- &w writes the configuration to memory
!--- Without this command the modem will lose its configuration
!--- when the modem is power cycled.
!--- We will now suspend the telnet session. For this, we will enter
!--- the escape sequence Ctrl-Shift-6 x (press Control-Shift-6, let go,
!--- then press x).
Closing connection to 172.22.53.145 [confirm]
!--- The disconnect command terminates the telnet session.
Use an analog phone to verify that the phone line is active and
functions properly. Then, connect the analog phone line to the modem.
Initialize an EXEC modem call to the router from another device
(such as, a PC) in order to test the modem connection.
Use a terminal emulation program on the PC, such as Hyperterminal,
and access the modem of the PC through one of the COM ports. When you are
connected to the modem of the PC through the COM port, initiate the dial to the
router. For an example, refer to
Note: The AUX port line does not run PPP. Therefore, for this
connection, you cannot use Microsoft Windows Dialup Networking (DUN) to dial.
When the connection is established, the dialin client is prompted
for a password. Enter the correct password.
Note: This password must match the one configured on the AUX port