2511 Console Server - Reverse telnet to console ports actually goes back to console server itself.

Posted on 2010-09-11
Last Modified: 2013-03-22
I have a 2511 that I configured and it was working fine.  Somewhere along the way I must have changed something that causes it to not work correctly.  I have 7 devices plugged in to ports 1-7, all of which I know work on the console port etc.  The issue is that when I issue a:

connect device and hit <enter>
connect lookback-address 2001 (or 2002, etc)

it actually connects me back to the Console server itself again.  I've changed the login message on the console server to confirm that it is in fact what I'm connecting to.

This did work so not sure what happened :(

I've attached the config.

Help very much appreciated!
Current configuration:


version 12.0

service config

service timestamps debug uptime

service timestamps log uptime

no service password-encryption


hostname xxxxxx


aaa new-model

aaa authentication login default local

aaa authentication enable default enable

aaa authorization exec default local

enable secret !

ip subnet-zero

no ip domain-lookup

ip host r2821a 2001

ip host r2821b 2002

ip host 3500a 2003

ip host 3500b 2004

ip host 5505a 2005

ip host apcnew1 2006

ip host apcold1 2007

ip host apcold2 2008




interface Loopback0

 ip address

 no ip directed-broadcast


interface Ethernet0

 ip address

 no ip directed-broadcast

 no ip mroute-cache

 no cdp enable


interface Serial0

 no ip address

 no ip directed-broadcast

 no ip mroute-cache


 no fair-queue


ip default-gateway

ip http server

ip classless

ip route



menu console_menu title ^CCC


      Console Access Server


        To disconnect a session, please press <CTRL><SHIFT>6 &

        enter X and then enter "18" to disconnect.

        Type a number to select an option;

        Type 17 to exit the menu.



        1.      R2821a          Console

        2.      R2821b          Console

        3.      3500a           Console

        4.      3500b           Console

        5.      1900a           Console

        6.      apc new         Console

        7.      apc old 1       Console

        8.      unused

        9.      unused

        10.     unused

        11.     unused

        12.     unused

        13.     unused

        14.     unused

        15.     unused

        16.     unused

        17.     Exit

        18.     Disconnect your present Serial connection


menu console_menu command 1 connect 2001

menu console_menu command 2 connect 2002

menu console_menu command 3 connect 2003

menu console_menu command 4 connect 2004

menu console_menu command 5 connect 2005

menu console_menu command 6 connect 2006

menu console_menu command 7 connect 2007

menu console_menu command 8 connect 2008

menu console_menu command 9 connect 2009

menu console_menu command 10 connect 2010

menu console_menu command 11 connect 2011

menu console_menu command 12 connect 2012

menu console_menu command 13 connect 2013

menu console_menu command 14 connect 2014

menu console_menu command 15 connect 2015

menu console_menu command 16 connect 2016

menu console_menu command 17 menu-exit

menu console_menu command 18 disconnect

menu console_menu clear-screen

menu console_menu status-line

menu console_menu line-mode

menu console_menu single-space

snmp-server community public RO

snmp-server community ReadOnly RO

banner incoming ^CConsole Server^C

banner motd ^CHappy Today^C


line con 0

 exec-timeout 0 0

line 1 16

 session-timeout 20

 no exec

 exec-timeout 0 0

 transport input all

line aux 0

 transport preferred telnet

 transport input all

 speed 38400

 flowcontrol hardware

line vty 0 4

 exec-timeout 120 0

 autocommand menu console_menu



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Question by:techeez
  • 3
LVL 24

Expert Comment

by:Ken Boone
ID: 33654895
So could it be that your devices do not have a timeout on them, and when you connect into say the device on port 2002, that that device is actually telnetted back to the terminal server ???  Just throwing some ideas out.  Have you physically checked the cabling?

Author Comment

ID: 33654950
Thanks for the thoughts.

The thing is though that it's the same for all 7 ports... I know that this did work!  I haven't explicitly retested the cables since this stopped working but I can't imagine that all 7 cables would become defective at one.

For the timeout... 5 of them are cisco devices and then the other 2 are APC masterswitches.  I think given that it's not working for any that it's pretty much got to be something on the 2511.
LVL 22

Accepted Solution

Jody Lemoine earned 500 total points
ID: 33655497
From the sounds of it, you're just getting the router's authentication prompt rather than an actual connection back to the router.  If you use the connect command and enter valid credentials for the router when it appears to loop back, does it take you to the 2511's IOS prompt or does it connect you to the device on the serial line.  If it's the latter, you just need to disable authentication to the ports, assuming that you're relying on the devices' own authentication.

aaa authentication login reverse-telnet none
aaa authorization reverse-access reverse-telnet none
line 1 16
 login authentication reverse-telnet
 authorization reverse-access reverse-telnet

Author Closing Comment

ID: 33655710
Thanks... That took care of it!

Author Comment

ID: 33658081
So the solution was bang on... just to add in case it's helpful for someone else I just hadn't ever waitied long enough after logging in to see that it was just authenticating me first on the console server and THEN passing me through to the 'console port'  I'm still not clear on what I did to change this as it didn't do it previously but at least it's working!  Thanks a lot Jody.

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