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Router Line Numbering 75
where 123.123.123.123 is the router's E0 port and 2001 is the Cisco reserved port number for
the first asynchronous port on the router. Table 4-3 shows the Cisco reserved port numbers for
all port ranges.
The use of the rotary group reserved port number connects to the first available port that is in
the designated rotary group. If a specific individual port is desired, the numbers from the first
column of Table 4-3 are used.
You can establish a session with an attached modem using reverse Telnet and the standard AT
command set (listed later in Table 4-4) to set the modem configuration. This, however, is the
hard way because once a modem connection has been established using reverse Telnet, you
must disconnect from the line for the modem to be usable again. In addition, to exit the
connection, you would have to press Ctrl+Shift+6 and then x to suspend the session, and then
issue the disconnect command from the router prompt. It is important to remember this simple
sequence because the modem does not understand the exit command as does a router!
Router Line Numbering
The line numbers on a router are obtained in a methodical manner. The console port is line 0.
Each asynchronous (TTY) port is then numbered 1 through the number of TTY ports on the
router. The auxiliary port is given the line number LAST TTY + 1, and the virtual terminal (vty)
ports are numbered starting at LAST TTY + 2.
Example 4-1 has the show line output for a Cisco 2511 router, which has eight asynchronous
ports available. Notice that the AUX port is labeled in line 17 and the vty ports are labeled in
lines 18­22.
Table 4-3
Reverse Telnet Cisco Reserved Port Numbers
Connection Service
Reserved Port Range
For Individual Ports
Reserved Port Range
For Rotary Groups
Telnet (character mode)
2000­2xxx
3000­3xxx
TCP (line mode)
4000­4xxx
5000­5xxx
Telnet (binary mode)
6000­6xxx
7000­7xxx
Xremote 9000­9xxx
10000­10xxx
Example 4-1
show line Output for Cisco 2511 Router
2511Router>show line
Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
* 0 CTY - - - - - 0 1 0/0 -
* 1 TTY 9600/9600 - - - - - 7 23 0/0 -
* 2 TTY 9600/9600 - - - - - 5 1 0/0 -
* 3 TTY 9600/9600 - - - - - 14 63 0/0 -
* 4 TTY 9600/9600 - - - - - 4 3 0/0 -
continues