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Community Member

Default number 20 in line numbers of Telnet

Hi guys,

telnet x.x.x.x 20yy

yy is the decimal line number to which you want to connect and 20 is default.

What's that 20 means?

May I know please?

Thanks!

=)

6 REPLIES

Re: Default number 20 in line numbers of Telnet

It's the virtual line number assigned by the device. A show line will show the virtual lines on the system.

Hope that helps.

Community Member

Re: Default number 20 in line numbers of Telnet

Yes, a show line command will show the virtual lines on the system, but once you ping the IP address it will also show you the virtual line WITH THAT NUMBER 20 inside a parenthesis. Am I right?

If it's line 34 it will say, when you're trying to ping, 2034.. Is that default number 20 (with virtual line 34) assigned by the device? Is that what you mean? Well, I still didn't get it. Apologize.

Thanks.. =)

Community Member

Re: Default number 20 in line numbers of Telnet

Hi guys please I need a little help.. Thanks.. =)

Bronze

Re: Default number 20 in line numbers of Telnet

Hi,

The number 20yy (ie 2034) is the TCP port number that you're connecting to

Normally when you telnet you go to port 23 but if you put a port number on the end you'll connect to another TCP socket. ie

telnet 10.1.1.1 goes to port 23

telnet 10.1.1.1 25 goes to smtp

telnet 10.1.1.1 80 goes to http

etc.

TCP ports 0-1023 are well known reserved port numbers and so cisco have just added 20 to the front of the line number in order to aviod the lower range of TCP ports.

Therefore the number 20 is just arbitary. See link below for a full list of TCP ports

http://www.iana.org/assignments/port-numbers

Regards

Re: Default number 20 in line numbers of Telnet

When you install a card with A/S lines, new lines are installed (ie 20-27 for an 8 port card). Here's a link on the line numbering by platform.

http://www.cisco.com/en/US/products/hw/routers/ps274/products_tech_note09186a00801ca70b.shtml

To establish a reverse Telnet session to an asynchronous line, determine the IP address of your LAN (Ethernet) interface or loopback address, then enter a Telnet command to port 2000 + n on the access server, where n is the installed asynchronous line number. For example, to connect to the console of the router attached to line 1 (which is really asynchronous line 20)-

router# telnet 172.16.1.10 2020

Trying 172.16.1.10, 2020 ... Open

router1>

The 2000 is something decided to use and AFAIK you can't change it.

Hope that helps.

Community Member

Re: Default number 20 in line numbers of Telnet

Thanks guys!

Thanks so much... =)

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