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This chapter describes use of physical and virtual terminals on the Cisco router/bridge product. These tasks include:
This chapter concludes with alphabetical summaries of the commands described in this chapter.
A TCP/IP Telnet connection is the basic way to communicate from a terminal to a host on a network. The Cisco Systems network servers provide Telnet communication as defined in RFC 854 and the MIL STD 1782 specification.
To start a Telnet connection, type a host name or a dotted-decimal Internet address at the EXEC prompt. You may precede the host name or Internet address with the command connect or telnet. This can be helpful if the host name you want to use conflicts with a network server command name.
The network server automatically numbers connections for you. Several commands use these numbers to identify connections, and you can display them using the where command described later in this chapter.
If you use a host name, the network server must first find the corresponding Internet address. To find this address, the network server searches its host-name-to-address cache. If the name is not in the cache, the network server uses a dynamic name lookup method. This method enables the network server to query a set of server hosts for the address.
As an option, you can specify a decimal TCP port number after the host name or Internet address when starting a Telnet connection. Normally, the network server uses the default Telnet server port, port number 23 (decimal).
After the network server determines the Internet address, or if you specify the address directly, the network server attempts to connect with the Telnet server port at that address. If the connection attempt fails, the network server displays a message to that effect and returns to the EXEC interpreter.
If the connection attempt succeeds, you can communicate with the server host as a terminal of that host. When you log off the host, the network server returns to the EXEC interpreter.
To connect to a host named router-1, you would simply type that name at the prompt, as seen in this example.
Gateway>router-1
This example illustrates how to connect to a router with IP address 103.81.25.2:
Gateway>connect 103.81.25.2
The network server provides an escape sequence with which you can leave a Telnet connection without terminating it and return to the EXEC interpreter. This allows you to have any number of concurrent Telnet connections open, and to switch back and forth between them. Follow these steps to switch between connections:
Step 1: Type the escape sequence, which is usually the default key sequence Ctrl-^, X. This sequence is entered by pressing the Ctrl and ^ keys simultaneously, letting go, then pressing the X key.
Step 2: At the system command prompt, type the command to open another connection.
To make a new connection, use the procedure described in the previous section, "Making Telnet Connections." To return to an existing connection, use the resume command. Use the where command to show your open connections.
You can change the first part of the escape sequence with the escape-character command; see the section "Setting the Escape Character" in the chapter, "Configuring the System."
Use the following command to get a listing of connections:
where
This command displays information about open connections associated with the current terminal line, as seen in the following example:
Gateway>where
Conn Host Address Byte Idle Conn Name
1 DREGGS 130.106.19.50 0 0 DREGGS
2 EMBER 130.106.20.33 0 0 EMBER
* 3 CLASH 130.106.21.24 0 0 CLASH
The information includes the connection number, host name, address, number of characters waiting to be sent to the terminal, idle time, and connection name. An asterisk (*) indicates the current connection.
Use the EXEC resume command to resume a connection. This command has the following syntax:
resume [connection]This command provides three ways to resume a previous connection:
The where command provides the connection number.
The following examples demonstrate use of the resume command.
This command resumes connection 2.
Gateway>resume 2
You can omit the command name and simply type the connection number to resume that connection. This example resumes connection 3.
Gateway>3
To resume the most recent connection, simply press the Return key.
To name a connection, use the following command:
name-connectionThis command assigns a logical name to a connection. The EXEC prompts for the connection number and name to assign when you enter this command. The where command displays a list of the assigned logical connection names.
To exit a session, use one of the following commands:
exit quitThe exit and quit commands terminate the incoming connection and all outgoing connections from the network server. Enter one of these commands when you are finished with all sessions.
To disconnect from a specified connection, use the following command:
disconnect [connection]The optional argument connection is a connection name or number; the default is the current connection.
Do not use the disconnect command to end a session. Instead, log off the host, thus allowing the host to initiate the disconnect. If you cannot log off the host, then use the
disconnect command.
To reset a terminal line, use the following privileged EXEC command:
clear line line-numberThis command aborts any connections, terminates the associated processes, and resets the data structures associated with a terminal line.
The argument line-number specifies the terminal line number.
In addition to the console terminal, each network server supports up to five incoming Telnet connections. Each of these connections can start an EXEC interpreter process on the network server.
The user of an incoming Telnet connection can gain access to the privileged EXEC commands through the enable command, which requires a password. With access to the complete EXEC command set, the incoming connection acts as a remote console. A remote console connection provides a convenient way to monitor and adjust network server operation.
You can control access to the network server with access lists; see the section "Configuring IP Access Lists" in the "Routing IP" chapter for more information.
The network server supports the following Telnet options:
To show the status of a TCP connection, enter this EXEC command:
show tcp [line-number]The show tcp command displays the status of all TCP connections. Specify the optional argument line-number in octal to display the status of the TCP connections for a particular line. The following example shows the command output:
con0 (console terminal), connection 1 to host MATHOM
Connection state is ESTAB, I/O status: 1, unread input bytes: 1
Local host: 192.31.7.18, 33537 Foreign host: 192.31.7.17, 23
Enqueued packets for retransmit: 0, input: 0, saved: 0
Event Timers (current time is 2043535532):
Timer: Retrans TimeWait AckHold SendWnd KeepAlive
Starts: 69 0 69 0 0
Wakeups: 5 0 1 0 0
Next: 2043536089 0 0 0 0
iss: 2043207208 snduna: 2043211083 sndnxt: 2043211483 sndwnd: 1344
irs: 3447586816 rcvnxt: 3447586900 rcvwnd: 2144 delrcvwnd: 83
RTTO: 565 ms, RTV: 233 ms, KRTT: 0 ms, minRTT: 68 ms, maxRTT: 1900 ms
ACK hold: 282 ms
Datagrams (max data segment is 536 bytes):
Rcvd: 106 (out of order: 0), with data: 71, total data bytes: 83
Sent: 96 (retransmit: 5), with data: 92, total data bytes: 4678
To show the current active sessions, use the following command:
show sessionsThe show sessions command provides information about open Telnet connections. This command may be run at the user-level prompt.
The show users and systat EXEC commands display information about the active lines of the network server, including the line number, connection names, and terminal location.
show users [all] systat [all]Specify the optional keyword all to display information for both active and inactive lines. These commands enable monitoring of virtual terminal use. You may issue these commands at the user-level prompt. They are synonymous.
The following sections describe how to change the terminal parameters using the terminal commands. The new settings temporarily override those made with the line configuration subcommands described in the section "Configuring Console and Virtual Terminal Lines" in the "Configuring the System" chapter.
To obtain information about the terminal configuration parameter settings for the current terminal line, use the show terminal command. To display information about the active ports of the server, use the show users command. The information displayed includes the line number, connection name, idle time, and terminal location.
Some terminal commands use the decimal representation of an ASCII character as an argument. See the "ASCII Character Set" chapter for ASCII-to-decimal conversion information.
To display a list of commands that you can enter to change the hardware and software parameters of the current terminal line, use the command:
terminal ?Each command has a no variation that undoes the local setting.
To set or unset the number of characters (columns) on a single line of the current terminal screen, use the terminal width command:
terminal width columns terminal no widthThe login protocol uses the argument columns to set up terminal parameters on a remote host.
This example sets the terminal width to 132 columns.
Gateway>terminal width 132
To set or unset the escape character for the current terminal line, use the terminal escapecharacter command:
terminal escape-character decimal-number terminal no escape-characterThe argument decimal-number is the ASCII decimal representation of the desired escape character or an escape character (Ctrl-P, for example). Typing the escape character followed by the X key returns you to the EXEC when you are connected to another computer. The default escape character is Ctrl-^. (See the "ASCII Character Set" chapter for a list of ASCII characters.)
The operating software interprets by pressing the Break key on the console as an attempt to halt the system.
This example sets Ctrl-P as the escape characters:
Gateway>terminal escape-character 17
To display the debug message on the console and terminals, use the terminal monitor command:
terminal monitor terminal no monitorThe terminal monitor command copies debug command output and system error messages to the current terminal as well as to the console terminal.
To use this command, you must first issue the enable command and enter the password to access the privileged command mode.
To set the character padding on the current terminal line, use the terminal padding commands:
terminal padding decimal-number count terminal no padding decimal-numberThe argument decimal-number is the ASCII decimal representation of the character. The argument count is the number of NULL bytes sent after that character. (see the "ASCII Character Set" chapter for a list of the ASCII characters.)
The terminal no padding command ends this padding.
This example pads RETURNS (ASCII character 25) with 20 NULL bytes:
Gateway>terminal padding 25 20
To display the configuration parameter settings for the current terminal, use this EXEC command:
show terminalThis command may be issued at the user-level prompt.
All Cisco internetworking products include a server which implements a subset of Digital Equipment Corporation's (DEC's) Maintenance Operation Protocol (MOP) for Ethernet interfaces. The MOP server supports the request ID message, periodic system ID messages, and the remote console carrier functions.
The MOP server periodically multicasts a system ID message, which is used by Digital's Ethernet configurator to determine what stations are present in an Ethernet network. The configurator is controlled by the Network Control Program (NCP) command define module configurator. For more information on this command, consult DECnet-VAX documentation.
The Cisco internetworking products use the MOP communication device code of 121. This code has been assigned to Cisco by Digital, although some versions of DECnet-VAX software may report the code numerically, rather than with a device name. The Digital Ethernim configurator product also makes use of receipt of system ID messages when building network maps.
The MOP server supports the Digital remote console function. In this capacity, a system manager on a DECnet system that does not include TCP/IP can create a virtual terminal connection to a Cisco router. The NCP commands connect node and connect via are used to connect to the remote console. Due to the nature of the MOP server, only a single inbound connection per Ethernet interface is supported. The MOP server does not contain the necessary mechanisms for supporting more than one connection at a time.
MOP is not a routable protocol. To bridge the MOP console carrier and system ID functions, enable bridging for protocol type 6002. The periodic system ID messages are sent to the multicast address AB00.0002.0000.
The EXEC command debug mop reports events occurring within the MOP server, including reception of request ID messages, transmission of system ID messages, and reservation and release of the remote console.
This section lists the EXEC commands described in this chapter in alphabetical order.
clear line line-number
Aborts connections and processes and resets the line. Argument line-number specifies the line.
{connect|telnet} [connection]
Either of the commands connects to a remote host using the Telnet protocol. The optional argument connection specifies a host name or an IP address.
disconnect [connection]
Closes the specified connection. The optional argument connection is a connection name or number; the default is the current connection.
exit
quit
Either of the commands terminates the EXEC command processor and closes any active Telnet sessions.
name-connection
Assigns a logical name to a connection. The EXEC prompts for the connection number and name to assign when you enter this command.
resume [connection]
Resumes a connection. The optional argument connection is a connection name or number.
show sessions
Provides information about open Telnet connections.
show users [all]
systat [all]
Displays information about active lines. The optional all keyword provides information about inactive as well as active ports.
show terminal
Displays information about the terminal configuration parameter settings for the current terminal line and the active ports of the server. The optional keyword all requests information for both active and inactive ports.
terminal ?
Lists commands you can enter to change hardware and software parameters of the current line.
terminal [no] escape-character decimal-number
Sets the escape character for the current terminal line. The argument decimal-number is either the ASCII decimal representation of the desired escape character or an escape character. The default escape character is Ctrl-^.
terminal [no] monitor
Displays the debug message on the console and terminals. It copies debug command output and system error messages to the current terminal as well as to the console terminal. To use this command, you must first issue the enable command and enter the password to access the privileged command mode.
terminal [no] padding decimal-number count
Sets the character padding on the current terminal line. The argument decimal-number is the ASCII decimal representation of the character. The argument count is the number of NULL bytes sent after that character. (See the "ASCII Character Set" chapter for a list of the ASCII characters.) The terminal no padding command ends this padding.
terminal [no] width columns
Sets the number of characters (columns) on a single line of the current terminal screen. The login protocol uses the argument columns to set up terminal parameters on a remote host.
where
Displays information about open connections associated with the current terminal line and provides the connection number.
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