Usage Guidelines
The table below lists the optional
telnet command keywords.
Table 1 telnet Keyword Options
Option
|
Description
|
/debug
|
Enables Telnet debugging mode.
|
/encrypt
kerberos
|
Enables an encrypted Telnet session. This keyword is available only if you have the Kerberized Telnet subsystem.
If you authenticate using Kerberos Credentials, the use of this keyword initiates an encryption negotiation with the remote server. If the encryption negotiation fails, the Telnet connection will be reset. If the encryption negotiation is successful, the Telnet connection will be established, and the Telnet session will continue in encrypted mode (all Telnet traffic for the session will be encrypted).
|
/ipv4
|
Specifies version 4 of the IP protocol. If a version of the IP protocol is not specified in a network that supports both the IPv4 and IPv6 protocol stacks, IPv6 is attempted first and is followed by IPv4.
|
/ipv6
|
Specifies version 6 of the IP protocol. If a version of the IP protocol is not specified in a network that supports both the IPv4 and IPv6 protocol stacks, IPv6 is attempted first and is followed by IPv4.
|
/line
|
Enables Telnet line mode. In this mode, the Cisco IOS software sends no data to the host until you press the
Enter key. You can edit the line using the standard Cisco IOS software command-editing characters. The
/line keyword is a local switch; the remote router is not notified of the mode change.
|
/noecho
|
Disables local echo.
|
/quiet
|
Prevents onscreen display of all messages from the Cisco IOS software.
|
/route:
path
|
Specifies loose source routing. The
path
argument is a list of hostnames or IP addresses that specify network nodes and ends with the final destination.
|
/source-interface
|
Specifies the source interface.
|
/stream
|
Turns on
stream processing, which enables a raw TCP stream with no Telnet control sequences. A stream connection does not process Telnet options and can be appropriate for connections to ports running UNIX-to-UNIX Copy Program (UUCP) and other non-Telnet protocols.
|
port-number
|
Port number.
|
bgp
|
Border Gateway Protocol.
|
chargen
|
Character generator.
|
cmd
rcmd
|
Remote commands.
|
daytime
|
Daytime.
|
discard
|
Discard.
|
domain
|
Domain Name Service.
|
echo
|
Echo.
|
exec
|
EXEC.
|
finger
|
Finger.
|
ftp
|
File Transfer Protocol.
|
ftp-data
|
FTP data connections (used infrequently).
|
gopher
|
Gopher.
|
hostname
|
Hostname server.
|
ident
|
Ident Protocol.
|
irc
|
Internet Relay Chat.
|
klogin
|
Kerberos login.
|
kshell
|
Kerberos shell.
|
login
|
Login (rlogin).
|
lpd
|
Printer service.
|
nntp
|
Network News Transport Protocol.
|
pim-auto-rp
|
Protocol Independent Multicast (PIM) auto-rendezvous point (RP).
|
node
|
Connect to a specific Local-Area Transport (LAT) node.
|
pop2
|
Post Office Protocol v2.
|
pop3
|
Post Office Protocol v3.
|
port
|
Destination local-area transport (LAT) port name.
|
smtp
|
Simple Mail Transfer Protocol.
|
sunrpc
|
Sun Remote Procedure Call.
|
syslog
|
Syslog.
|
tacacs
|
Specifies TACACS security.
|
talk
|
Talk (517).
|
telnet
|
Telnet (23).
|
time
|
Time (37).
|
uucp
|
UNIX-to-UNIX Copy Program (540).
|
whois
|
Nickname (43).
|
www
|
World Wide Web (HTTP, 80).
|
With the Cisco IOS implementation of TCP/IP, you are not required to enter the
connect or
telnet command to establish a terminal connection. You can enter only the learned hostname--as long as the following conditions are met:
To display a list of the available hosts, use the
show
hosts command. To display the status of all TCP connections, use the
show
tcp
command.
The Cisco IOS software assigns a logical name to each connection, and several commands use these names to identify connections. The logical name is the same as the hostname, unless that name is already in use, or you change the connection name with the
name-connection EXEC command. If the name is already in use, the Cisco IOS software assigns a null name to the connection.
The Telnet software supports special Telnet commands in the form of Telnet sequences that map generic terminal control functions to operating system-specific functions. To issue a special Telnet command, enter the escape sequence and then a command character. The default escape sequence is Ctrl-^ (press and hold the Ctrl and Shift keys and the 6 key). You can enter the command character as you hold down Ctrl or with Ctrl released; you can use either uppercase or lowercase letters. The table below lists the special Telnet escape sequences.
Table 2 Special Telnet Escape Sequences
Escape Sequence1
|
Purpose
|
Ctrl-^
b
|
Break
|
Ctrl-^
c
|
Interrupt Process (IP and IPv6)
|
Ctrl-^
h
|
Erase Character (EC)
|
Ctrl-^
o
|
Abort Output (AO)
|
Ctrl-^
t
|
Are You There? (AYT)
|
Ctrl-^
u
|
Erase Line (EL)
|
1 The caret (^) symbol refers to Shift-6 on your keyboard.
At any time during an active Telnet session, you can list the Telnet commands by pressing the escape sequence keys followed by a question mark at the system prompt:
Ctrl-^ ?
A sample of this list follows. In this sample output, the first caret (^) symbol represents the Ctrl key, and the second caret represents Shift-6 on your keyboard:
router> ^^?
[Special telnet escape help]
^^B sends telnet BREAK
^^C sends telnet IP
^^H sends telnet EC
^^O sends telnet AO
^^T sends telnet AYT
^^U sends telnet EL
You can have several concurrent Telnet sessions open and switch among them. To open a subsequent session, first suspend the current connection by pressing the escape sequence (Ctrl-Shift-6 then x [Ctrl^x] by default) to return to the system command prompt. Then open a new connection with the
telnet
command.
To terminate an active Telnet session, enter any of the following commands at the prompt of the device to which you are connecting:
close
disconnect
exit
logout
quit
Examples
The following example establishes an encrypted Telnet session from a router to a remote host named host1:
router>
telnet host1 /encrypt kerberos
The following example routes packets from the source system host1 to example.com, then to 10.1.0.11, and finally back to
host1 :
router>
telnet host1 /route:example.com 10.1.0.11 host1
The following example connects to a host with the logical name host1:
router>
host1
The following example suppresses all onscreen messages from the Cisco IOS software during login and logout:
router>
telnet host2 /quiet
The following example shows the limited messages displayed when connection is made using the optional
/quiet keyword:
login:User2
Password:
Welcome to OpenVMS VAX version V6.1 on node CRAW
Last interactive login on Tuesday, 15-DEC-1998 11:01
Last non-interactive login on Sunday, 3-JAN-1999 22:32
Server3)logout
User2 logged out at 16-FEB-2000 09:38:27.85