How to connect a modem into the AUX or CON port?

Here are the steps in setting up a US Robotics Modem to work on a Cisco AUX or CON port.

1. Connect a RJ45 to DB25 adapter to the modem and label it as modem.

RJ45 to DB25 Adapter Pinout

RJ45 DB25
1 Blue 4
2 Orange 20
3 Black 2
4 Red 7
5 Green 7
6 Yellow 3
7 Brown 8
8 White 5

2. Connect a Roll-Over cable from the RJ45-DB25 to the AUX/CON port of the router. Label the cable as Rollover.

RJ45 to RJ45 RollOver Cable Pinout

RJ45 RJ45
1 8
2 7
3 6
4 5
5 4
6 3
7 2
8 1

3. On the modem, set ONLY the seven pin down and re power the modem. This will restore the modem to factory defaults.

4. Now, set Pin 1,3, and 8 down on them modem. Then power cycle the modem again.

5. Console into the Router and telnet into the AUX/CON line to configure the modem. If there isn’t any IP setup on the router, you will need to add an IP address. Use a Loopback interface. Example:

router>config t

router(config)#int loopback0

router(config-if)#ip address

router(config-if)#no shutdown



4. Type in ‘show line’ in the router to see which line the modem is connected into.

5. If the line number is ’65’, you will need to add 2000 to the number. Exampel: telnet 2065

6. Once you have telnet into the modem, type in the following commands



* If you don’t get the ‘OK’ afterward, then there might be something wrong with the modem hardware or cable. Double check them.

7. Turn off the modem and change only Pin 1, 4, 6, and 8 to down

8. Turn on the modem and connect an analog line into it.

9. This set will configure the router to accept connection from the modem.

maui-rtr-10(config)#line con 0

!– Authenticate incoming connections using the password configured on the line.
!– This password is configured below:

maui-rtr-10(config-line)#password cisco

!– The router will use this password (cisco) to authenticate incoming calls.
!– For security purposes, replace “cisco” with a password that is not well known.

maui-rtr-10(config-line)#exec-time 5 0

!– Set the exec timeout to be 5 minutes and 0 seconds
!– This exec timeout clears the EXEC session after 5 minutes of inactivity
!– For information refer to the Modem-Router Connection Guide

maui-rtr-10(config-line)#speed 9600

!— console line speed that should be used to communicate with the modem
!— This speed matches the DTE speed configured in the init string (&u6)
!— Refer to the section Miscellaneous for more information

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 command enable secret password to setup the enable password.

10. Test the modem connection with another PC.