In this section, you are presented with the information to configure the features described in this document.

Note: To find additional information on the commands used in this document, use the Command Lookup Tool ( registered customers only) .

A terminal or comm server commonly provides out-of-band access for multiple devices. A terminal server is a router with multiple, low speed, asynchronous ports that are connected to other serial devices, for example, modems or console ports on routers or switches.

The terminal server allows you to use a single point to access the console ports of many devices. A terminal server eliminates the need to configure backup scenarios like modems on auxiliary ports for every device. You can also configure a single modem on the auxiliary port of the terminal server, to provide dial-up service to the other devices when network connectivity fails.

This document shows how to configure a terminal server to access only the console ports on other routers through Reverse Telnet. Reverse Telnet allows you to establish a Telnet connection out on the same device you telnet from, but on a different interface. For more information on Reverse Telnet refer to Establishing a Reverse Telnet Session to a Modem.

The Cisco 2509 - 2512 series routers use a 68-pin connector and breakout cable. This cable (CAB-OCTAL-ASYNC) provides eight RJ-45 rolled cable async ports on each 68-pin connector. You can connect each RJ-45 rolled cable async port to the console port of a device. The 2511 router allows for a maximum of 16 devices to be remotely accessible. In addition, the NM-16A or NM-32A high density async network modules are available for the Cisco 2600 and 3600 series routers to provide the same function. For more information on cabling refer to the Let's Connect:Your Serial Cable Guide and the Cabling Guide for Console and AUX Ports.

Note: The async ports from the 68-pin connector are data terminal equipment (DTE) devices. DTE to DTE devices require a rolled (null modem) cable and DTE to data circuit-terminating equipment (DCE) devices require a straight-through cable. The CAB-OCTAL-ASYNC cable is rolled. Therefore, you can connect each cable directly to the console ports of devices with RJ-45 interfaces. However, if the console port of the device to which you connect is a 25-pin interface (DCE), you must use the RJ-45 to 25-pin adapter marked "Modem" (to reverse the "roll") in order to complete the connection.

This document uses this network setup:

This document uses this configuration:

aus-comm-server#show running-config
!
version 12.0

service timestamps debug datetime msec localtime show-timezone
service timestamps log datetime msec localtime show-timezone
service password-encryption
!
hostname aus-comm-server
!
enable secret  <deleted>
!
username cisco password <deleted>
!
ip subnet-zero
ip domain-list cisco.com
no ip domain-lookup

ip host 3600-3 2014 172.21.1.1

!--- The host 3600-3 is connected to port 14 of the comm server.
!--- Ensure that the IP address is that of an interface on the comm server.

ip host 3600-2 2013 172.21.1.1
ip host 5200-1 2010 172.21.1.1
ip host 2600-1 2008 172.21.1.1
ip host 2509-1 2007 172.21.1.1
ip host 4500-1 2015 172.21.1.1
ip host 3600-1 2012 172.21.1.1
ip host 2511-2 2002 172.21.1.1
ip host 2511-rj 2003 172.21.1.1
ip host 2511-1 2001 172.21.1.1
ip host 5200-2 2011 172.21.1.1
ip host 2520-1 2004 172.21.1.1
ip host 2520-2 2005 172.21.1.1
ip host 2600-2 2009 172.21.1.1
ip host 2513-1 2006 172.21.1.1
ip host pix-1 2016 172.21.1.1
!
!
process-max-time 200
!
interface Loopback1
ip address 172.21.1.1 255.0.0.0

!--- This address is used in the IP host commands.
!--- Work with loopback interfaces, which are virtual and always available.

no ip directed-broadcast
!
interface Ethernet0
ip address 171.55.31.5 255.255.255.192

!---  Use a public IP address to ensure connectivity.

No ip directed-broadcast
no ip mroute-cache
!
interface Serial0
no ip address
no ip directed-broadcast
no ip mroute-cache
shutdown
!
ip default-gateway 171.55.31.1

!--- This is the default gateway when routing is disabled.
!--- For example, if the router is in boot ROM mode.

ip classless
ip route 0.0.0.0 0.0.0.0 171.55.31.1

!--- Set the default route for the external network.

no ip http server
!
line con 0
transport input all
line 1 16
session-timeout 20

!--- The session times out after 20 minutes of inactivity.

no exec

!--- Unwanted signals from the attached device do not launch.
!--- An EXEC session ensures that the line never becomes unavailable
!--- due to a rogue EXEC process.

exec-timeout 0 0

!--- This disables exec timeout transport input all.
!--- Allow all protocols to use the line.
!--- Configure lines 1 - 16 with at least transport input Telnet.

line aux 0

!--- Auxiliary port can provide dial backup to the network.
!--- Note: This configuration does not implement modem on AUX port modem InOut.
!--- Allow auxiliary port to support dialout and dialin connections.

transport preferred telnet
transport input all
speed 38400
flowcontrol hardware
line vty 0 4
exec-timeout 60 0
password <deleted>
login
!
end