Cisco fun

Wednesday, April 20, 2005

Cisco fun

So I was testing some stuff in my lab for a friend of mine, and I discovered an alternate use of the AUX port on your Cisco router.
Actually I've always been aware of the AUX port, but only thought it would apply for some modem callback stuff.

Here's a cool way to use your AUX port:


r3#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
r3(config)#int loopback 0
r3(config-if)#ip address 10.10.10.10 255.255.255.255
r3(config-if)#no shutdown
r3(config-if)#exit 
r3(config)#line aux 0
r3(config-line)#transport input telnet
r3(config-line)#^Z
r3#

r3#sh line
 Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
   0 CTY              -    -      -    -    -      1       0     0/0       -
*   65 AUX   9600/9600  -    -      -    -    -     14       2     0/2517358   -
*   66 VTY              -    -      -    -    -     14       0     0/0       -
  67 VTY              -    -      -    -    -      0       0     0/0       -
  68 VTY              -    -      -    -    -      0       0     0/0       -
  69 VTY              -    -      -    -    -      0       0     0/0       -
  70 VTY              -    -      -    -    -      0       0     0/0       -

Line(s) not in async mode -or- with no hardware support:
1-64

I'll now plugin a rollover cable in the AUX port, and the other end into the console port of some other device (in this case a Cat5)

Now I'll be able to do the following:


r3#telnet 10.10.10.10 2065
Trying 10.10.10.10, 2065 ... Open

Console>
Console> sh ver
WS-C5505 Software, Version McpSW: 6.3(4a) NmpSW: 6.3(4a)
Copyright (c) 1995-2002 by Cisco Systems
NMP S/W compiled on Feb  9 2002, 19:11:26
MCP S/W compiled on Feb 09 2002, 18:56:22

System Bootstrap Version: 5.1(1)

Hardware Version: 1.0  Model: WS-C5505  Serial #: xxxxxxxxx

Mod Port Model      Serial #  Versions
--- ---- ---------- --------- ----------------------------------------
1   2    WS-X5550   022301142 Hw : 1.2
                            Fw : 5.1(1)
                            Fw1: 5.2(1)
                            Sw : 6.3(4a)

     DRAM                    FLASH                   NVRAM
Module Total   Used    Free    Total   Used    Free    Total Used  Free
------ ------- ------- ------- ------- ------- ------- ----- ----- -----
1       32768K  18662K  14106K   8192K   3910K   4282K  512K  185K  327K

Uptime is 0 day, 5 hours, 30 minute

Pretty nifty, If you need console access to a device that is behind a core-router..

1 comment:

Anonymous said...: That you described is a "reverse telnet" conenction. You can do it on any asyncronus port of Cisco routers (I.E. Console port, AUX port, serial port in Async mode).

It is very userful to manage a device remotely without telnet limitations (I.E. You cannot do a pass. recovery via telnet).

For example:You want to fully manage a device (device B) via console port but you cannot physically access it. You can connect CON port of device B to the AUX, CON or serial ASYNC inteface of another device (device A). Then you remotely access device A via telnet and, from device A you issue a "reverse telnet" to device B: it will be the same as connecting to device B via console Cable.
On Cisco web site (WWW.CISCO.COM) you will find a lot of docs about this tecnique (I.E. cable specifications, commands, ...).
Another nice thing is that you can configure a menu on device A, that acts as a terminal server, to simplify console connections to many other devices (as many as async ports you have, including the AUX one).
Enjoy.; 5:02 PM