'Lines' are physical async serial ports on the router (such as a terminal or modem), a virtual network connection, or another type of serial line on the router. To see which lines you have on your router, use the show line command:

Cell_Router#show line

Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
0 CTY - - - - - 0 0 0/0 -
1 TTY 9600/9600 - - - - - 20 31 1396/4188 -
2 TTY 9600/9600 - - - - - 15 36 0/0 -
3 TTY 9600/9600 - - - - - 13 34 1415/4246 -
4 TTY 9600/9600 - - - - - 8 38 1408/4229 -
5 TTY 9600/9600 - - - - - 8 45 1410/4232 -
6 TTY 9600/9600 - - - - - 6 38 1412/4237 -
7 TTY 9600/9600 - - - - - 5 39 2535/7604 -
8 TTY 9600/9600 - - - - - 6 12 2528/7583 -
9 TTY 9600/9600 - - - - - 8 15 2504/7514 -
10 TTY 9600/9600 - - - - - 8 11 1610/4828 -
11 TTY 9600/9600 - - - - - 5 19 2515/7547 -
12 TTY 9600/9600 - - - - - 4 9 2523/7568 -
13 TTY 9600/9600 - - - - - 4 8 2522/7565 -
14 TTY 9600/9600 - - - - - 4 6 2603/7804 -
15 TTY 9600/9600 - - - - - 4 6 2537/7610 -
16 TTY 9600/9600 - - - - - 5 8 2536/7607 -
17 AUX 9600/9600 - - - - - 0 0 0/0 -
* 18 VTY - - - - - 129 0 0/0 -
19 VTY - - - - - 24 0 0/0 -
20 VTY - - - - - 2 0 0/0 -
21 VTY - - - - - 1 0 0/0 -
22 VTY - - - - - 1 0 0/0 -

Use the show line summary command to get a summary:

Cell_Router#show line summary
0: ?uuu uuuu uuuu uuuu u?u- ---

17 character mode users. (U)
2 lines never used (?)
17 total lines in use, 17 not authenticated (lowercase)

As you can see from the example, the router has one console line (labeled CTY), one AUX port (labeled AUX), five VTY lines, and 16 TTY lines. Each is a different type of line.

The CTY port is a serial port, so you must have a PC/laptop with a serial interface and connect to the console with a rolled cable, most likely, using a DB9 to RJ45 adapter to connect from the serial port on your computer to the console port. Once you've used the console port to configure the router's network configuration, it isn't common to have to use it again. However, it's good to know that it's there if anything ever goes wrong. In addition, you should secure the console port to keep someone from connecting to it when you aren't around.

While not all routers these days have an AUX port, the AUX port is the auxiliary. Think of it as a secondary console port. The AUX ports don't get a lot of use except to access the router if locked out of the console port. In the past, network admins would connect modems to the AUX ports so they could dial into their routers. Like the console port, the AUX port is a serial port, and you should also take steps to secure it.

To have a TTY line on your router, you must have an ASYNC card in your router. This card provides some number of asynchronous serial ports on the router, which you can use for serial printers, serial modems, or dumb ASCII text terminals. With those ports, the serial printers could become networked printers (using the LPD service on the router), and the dumb terminals could become networked Telnet devices.

In the case of the router shown above, it has a 32-port asynchronous serial card (Cisco NM-32A ) installed, and it's using many of those ports for asynchronous serial devices such as ASCII text printers and ASCII test dumb terminals.

VTY ports are virtual TTY ports, used to Telnet or SSH into the router over the network. You can use them to connect to the router to make configuration changes or check the status. Most routers have five VTY ports, numbered 0 to 4. That means you can have up to five concurrent network admins configuring the router at one time. However, you can easily generate more VTY lines. For example, to create a total of 21 VTY lines (numbered 0 through 20), enter the following:

Cell_Router(config)# line 0 20

Here's the simplest and most useful configuration for your router lines:

Cell_Router(config)# line con 0
Cell_Router(config)# line aux 0
Cell_Router(config)# line vty 0 4
Cell_Router(config-line)# password !somethingHard$
Cell_Router(config-line)# logging synchronous
Cell_Router(config-line)# exec-timeout 60 0

On VTY lines:

Cell_Router(config-line)# transport input

You can always use the 'clear line' command to clear out a connection on a router line if you run into a problem.

To look at the terminal configurations of individual lines, use the show line command (even if you aren't connected to that line):

Cell_Router#show line console 0

Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
0 CTY - - - - - 0 0 0/0 -

Line 0, Location: "", Type: ""
Length: 24 lines, Width: 80 columns
Status: Ready
Capabilities: none
Modem state: Ready
Special Chars: Escape Hold Stop Start Disconnect Activation
^^x none - - none
Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch
00:10:00 never none not set
Idle Session Disconnect Warning
never
Login-sequence User Response
00:00:30
Autoselect Initial Wait
not set
Modem type is unknown.
Session limit is not set.
Time since activation: never
Editing is enabled.
History is enabled, history size is 10.
DNS resolution in show commands is enabled
Full user help is disabled
Allowed input transports are none.
Allowed output transports are pad v120 telnet rlogin.
Preferred transport is telnet.
No output characters are padded
No special data dispatching characters

We hope this helps with configuring Lines in Cisco IOS.

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