Cisco IOS in a Nutshell, 2nd Edition

Name

transport — line

Synopsis

transport input protocol
transport output protocol
transport preferred protocol

Configures

The transport protocol

Default

Output and preferred, telnet; input, none

Description

This command specifies the transport protocol the router should use. input specifies the protocol to use for incoming connections on a line; output is for output connections on a line; and preferred is the transport protocol to use when the user does not specify one.

Using the command transport preferred none helps to prevent typos at the command line from causing a bogus DNS lookup. (With the default output setting, a mistyped command is frequently interpreted as a hostname for the telnet, initializing a DNS lookup.)

The protocol parameter specifies which protocol to use; possible values are given in Table 17-27.

Table 17-27. Transport protocols

Protocol	Meaning
lat	DEC LAT protocol, when connecting to DEC hosts
mop	Maintenance operation protocol
nasi	Netware asynchronous services interface protocol
none	No protocol selection is to be made on this line
rlogin	The Unix rlogin protocol
telnet	TCP/IP telnet protocol
ssh	SSH (Secure Shell)
all	All in the list
v120	ISDN asynchronous protocols

Example

Routers do not allow incoming network connections to a TTY by default, so you must use the transport input command to enable this feature:

line tty 2
  transport input all