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m4rtin
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connect from AUX port to CON port

Wed May 09, 2012 5:17 am

One is able to connect from first Cisco router to console port of second Cisco router(routers are connected with rollover cable) using for example following configuration on the first router:

!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Loopback12345
ip address 10.10.10.1 255.255.255.0
!
line con 0
line aux 0
modem InOut
transport input all
line vty 0 4
no login
!


..and executing "telnet 1.1.1.1 2001" or "telnet 10.10.10.1 2001" in the first router if AUX line is 1. If there is for example IP address 192.168.1.75 on a physical interface of the first router, then "telnet 192.168.1.75 2001" works as well. Is there some sort of technical reason behind telneting to IP and such certain port? Or is it just the way this works in Cisco devices?

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Agent Zed
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Re: connect from AUX port to CON port

Sat May 12, 2012 4:52 am

To set Cisco router as a console server you need this bad boy: http://www.cisco.com/en/US/products/hw/ ... 93f0.shtml
I think that connecting con to aux will fry one of them, not sure, never tried to...

bertschs
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connect from AUX port to CON port

Sat May 12, 2012 9:06 pm

You don't need the NM card for a Cisco router to act as a console/terminal server if you just need one port. You just need an aux port. The NM card just gives you a ton of aux ports.

On Cisco devices, the console port has been solely an RS-232 out-of-band management port.

On the other hand, the aux port allows both incoming and outgoing sessions, and even allows you to tie the port to an Async interface, which can be used to terminate dial-up SLIP/PPP sessions using an attached analog modem, ISDN terminal adapter, etc.

The pin-out on the RJ45 ports is identical between console and aux ports, and uses a DTE/DCE agnostic pin-out. The pins were laid out so that by "rolling over" the cable (e.g. Pin 1 goes to pin 8, 2:7, 3:6, 4:5), you can make two ports with the same pinout communicate.

E.g., CTS and RTS pins like to go together, so they're on pins 1&8. TxD and RxD like to go together, so they're on pins 3&6, and so on.

In short, if you want to connect a con to an aux, both of which are pinned out identically, you just need to use a rollover cable. It will not fry anything. They're both RS-232 ports, so they're meant to go together.

If you have a rack full of Cisco routers, you can even daisy-chain them. Device#1 Aux to Device#2 Con, Device#2 Aux to Device#3 Con, etc.

bertschs
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connect from AUX port to CON port

Sat May 12, 2012 9:19 pm

Also, addressing the original question, there is no technical reason for using that specific port number, it is just what they chose.

The port number is actually 2000 plus the line number. E.g. Line 1 is 2001, line 49 is 2049.

Also, 2,000 is the base you use for standard telnet. They also have:
3000 for telnet with rotary
4000 for raw TCP
5000 for raw TCP with rotary
6000 for binary mode telnet
7000 for binary mode telnet with rotary
9000 for xremote
10000 for xremote with rotary

There is also a recent enhancement to connect using SSH.

E.g. To connect to line 27, you do:

ssh -l username:27 router.address

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Agent Zed
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Re: connect from AUX port to CON port

Mon May 14, 2012 2:05 am

What you know 'try' is a key to learn something new, not sure what I can use a single console port, but I sure will try it out :)

'

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