David Sudjiman

You have your router connected to internet, in this scenario you’re using 2501 (GW), and you need to ask your friend to troubleshoot your second router, a 2503 (R1), that seems has problem connecting to GW.

You can take advantage the use of AUX port.

To prepare, you need a rollover RJ45 cable and connect both routers using AUX port and put these configuration lines.

hostname GW
!
interface Loopback0
 ip address 192.168.1.1 255.255.255.255
!
! enable secret gw_secret
enable secret 5 $1$jrfJ$emVdO4/QA133es8FFR5XU/
!
line aux 0
 password gw_aux
 login
 modem InOut
 transport input all
 speed 38400
 flowcontrol hardware

On GW, that Loopback0 exists because GW does not have any IP address. For this scenario, you can use any available IP on your GW if there is any.

hostname R1
!
! enable secret r1_secret
enable secret 5 $1$jrfJ$emVdO4/QA133es8FFR5XU/
!
line aux 0
 password r1_aux
 login
 modem InOut
 transport input all
 speed 38400
 flowcontrol hardware

You need to check on what port your AUX port is.

GW#sh line
   Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
*    0 CTY              -    -      -    -    -      6       0     0/0       -
     1 AUX  38400/38400 - inout     -    -    -      6       0     0/4135    -
     2 VTY              -    -      -    -    -      0       0     0/0       -
     3 VTY              -    -      -    -    -      0       0     0/0       -
     4 VTY              -    -      -    -    -      0       0     0/0       -
     5 VTY              -    -      -    -    -      0       0     0/0       -
     6 VTY              -    -      -    -    -      0       0     0/0       -

From the above sh line result you see that AUX is on port 1. Cisco arranges the TCP port correspond with your AUX port by using port starting from port 2000. Now try to connect to particular TCP port 2001.

GW#telnet 192.168.1.1 2001
Trying 192.168.1.1, 2001 ... Open

User Access Verification

Password: gw_aux
Password OK

User Access Verification

Password: r1_aux
R1>ena
Password: r1_secret
R1#

Now, you can see that you can connect to R1 from GW using AUX port. to get out from R1 but not disconnecting the line, you use sequence CTRL+SHIFT+6 x. That is you press CTRL+SHIFT+6 altogether then you press x or you can use other sequence CTRL+ALT+6 x, depends your terminal application.

Currently, the session between GW and R1 exists, you can’t connect to R1 using telnet command.

GW#telnet 192.168.1.1 2001
Trying 192.168.1.1, 2001 ...
% Connection refused by remote host

GW#sh line
   Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
*    0 CTY              -    -      -    -    -      6       0     0/0       -
*    1 AUX  38400/38400 - inout     -    -    -      6       0     0/4135    -
     2 VTY              -    -      -    -    -      0       0     0/0       -
     3 VTY              -    -      -    -    -      0       0     0/0       -
     4 VTY              -    -      -    -    -      0       0     0/0       -
     5 VTY              -    -      -    -    -      0       0     0/0       -
     6 VTY              -    -      -    -    -      0       0     0/0       -

Can use that * mark on AUX port, that’s the sign that port AUX (and console) is in use. You can go back to R1 by pressing ENTER then you will be redirected to R1 again.

GW#
[Resuming connection 1 to 192.168.1.1 ... ]

R1#

When you finish configuring R1, you can’t close the connection from R1. You need to get out from R1 using sequence CTRL+SHIFT+6 x and from GW you need to close the session.

GW#disconnect
Closing connection to 192.168.1.1 [confirm]

GW#sh line
   Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
*    0 CTY              -    -      -    -    -      7       0     0/0       -
     1 AUX  38400/38400 - inout     -    -    -      7       0     0/4135    -
     2 VTY              -    -      -    -    -      0       0     0/0       -
     3 VTY              -    -      -    -    -      0       0     0/0       -
     4 VTY              -    -      -    -    -      0       0     0/0       -
     5 VTY              -    -      -    -    -      0       0     0/0       -
     6 VTY              -    -      -    -    -      0       0     0/0       -

Just in case the command disconnect does not work, you can force closing the session using command clear line 1.