Common Configuration Items

This section summarizes the configuration items you are likely to encounter when configuring a line on a router or a terminal server.

4.8.1. Communication Parameters

These useful commands set the low-level physical parameters of a line. To set the line speed (baud) you can use the speed, txspeed, or rxspeed commands. For databits, stop bits, and parity, use the commands databits, stopbits, and parity, respectively. For automatic baud rate detection , use the autobaud command.

For flow control, use the flowcontrol command, which takes as arguments none, software, or hardware. In a modern environment, hardware flow control is almost always appropriate.

4.8.2. Transport Type

The transport command defines which protocols can be used to connect to a line. The default protocol is none, which means that no incoming connections are allowed. The command transport input telnet specifies that telnet can be used as an incoming protocol, but no other protocols are allowed.

You can also specify the preferred protocol to use after a user has connected to a line. By default, the preferred protocol is telnet. Therefore, when users are connected to the router, they can type a hostname, and the router will assume they want to telnet to a device. To disable this behavior, use the command transport preferred none.

4.8.3. Session Limits and Timeouts

IOS provides two ways to limit the number of ongoing sessions. To limit the number of sessions allowed on a line, use the session-limit command. To limit a session's idle time, use the session-timeout command. If the session is idle longer than the specified time, the router automatically logs the user out. Note that these commands apply to the configuration of lines and not to the router as a whole.

4.8.4. Special Characters and Key Sequences

IOS allows you to specify a number of special characters that control the interaction between a user and the router. The activation character is the character that starts a terminal session when it is typed at a vacant terminal. The default activation character is Enter; you can set it to another value using the activation-character command. Other special characters are the disconnect character and the hold character, both of which have no defaults. The disconnect character disconnects (terminates) a session, while the hold character pauses a session until any other key is pressed. These characters are set using the disconnect-character and hold-character commands.

All three of these commands apply to lines; the argument for each command is the ASCII value for the character. For example, to set the disconnect character for line 2 to Ctrl-d (ASCII value 4), use the following commands:

Router(config)#line 2
Router(config-line)#disconnect-character 4