How to test Reverse Telnet


#1

This article applies for ES440, GX440 and LS300 AirLink modems.

Cable required

When using a blue console cable to connect to a Cisco router, you must use an additional NULL modem DB9 adapter, ending in a DB9 Male connector that will be attached to the AirLink device’s serial port.
For other router vendors, the adapter may be required, depending on the router’s console port.

Typical console cables


AirLink devices support a DCE Female DB9. See DB9 pin-out at the end of this article.

Setting up Reverse Telnet with Auto login Enabled

The following illustration shows a standard OOB connection between AirLink device and a router:

Go to ACEmanager > Serial: Port Configuration and set Startup Mode Default to “Reverse Telnet”.
Autologin Reverse Telnet is enabled by default. This means that ALEOS does not require additional user name and password. It passes the remote OOB communication directly to the router. Setup the Serial port parameters as per the router specifications. This is typically 9600,8N1. Device port in this example is 12345. This is the TCP port or Telnet port used to establish the OOB connection. To save the configuration, click “Apply” and then reboot the device.

To test Reverse Telnet functionality, use the command prompt or any other Telnet application (such as putty.exe or TeraTerm). For this example, we opened a Telnet session using the WAN IP address of the device 166.10.10.10 on the same port specified in ACEmanager as Device port.

C:>Telnet 166.10.10.10 12345

A message similar to this is displayed:


If the cable is correct and the router is accepting OOB messages, it prompts for the router user and password.

Setting up Reverse Telnet with Auto login Disable

This configuration is shown in the screen-shot below. When Autologin Reverse Telnet is set to “Disable”, you must provide ALEOS login credentials (username: sconsole, and password: 12345) as an extra authentication step when attempting the connection to the router. After you enter the ALEOS credentials, you are prompted for the router’s console login credentials username and password.

To test the connection from a computer to the router’s console port, use:

C:>Telnet 166.10.10.10 12345

ALEOS requires authenticating with a dedicated Reverse Telnet login :sconsole and password:12345. After that, it prompts for the router’s console login.

Known issue: Please do not use user: user and password: 12345. If these are used, the device establishes a normal AT command session.

Reverse Telnet and VPN

When the AirLink device is connected to a VPN, assuming it has the default device IP 192.168.13.31, you can access the OOB router on the serial console port from a computer on the VPN network using:
Telnet 192.168.13.31 12345. Please note that it is using the Local LAN IP or Device IP address.
The connection is redirected to the device’s serial port, which in turn makes the connection to the router, as shown below:

*If the device has VPN Split tunnel enabled, it means that in ACEmanager Out of Bounds is set to “Allowed”. It is possible to access the OOB router’s console port using the device’s Public WAN IP address, for example, 166.1010.10 12345 (or Telnet WAN IP 12345).

Troubleshooting

I am attempting a Telnet connection on a specified port, but the connection times out.

There are several possible reasons for this. First of all, the device should have a Public IP that can be accessed from the Internet. Try accessing the device using ACEmanager on port 9191, and then try to make the connection using Telnet on default ALEOS port 2332 (Telnet WAN IP 2332). If that works, the problem is that the Device port is not correctly setup on the AirLink device, or the Device port is blocked by any of the firewalls in the path of communication. Try setting up another Device port using a high port number.

I have a Telnet connection established on specified port, but it does not prompt for the router’s console login credentials.

Check the console cable. Reverse Telnet has been proven to be a fairly stable feature, however hardware issues arise in the field mostly because of incorrect console cables or DB9 adapters. Be sure to use console cables specified by the router’s manufacturer. In most of the cases, a DB9 null adapter is required.

Autologin is disabled. I can connect to ALEOS software, but I am not able to login in to the router.

Known issue: If you type the default user (user), and password (12345) you will be logged into an AT command session, and it will not connect to the console router. Please enter the expected Reverse Telnet user credentials, which are: user: sconsole and password: 12345 to begin the Reverse Telnet session.

How do I close a telnet session?

From a terminal window, you can use
Escape Character is ‘CTRL+]’
Microsoft Telnet> quit

How do I finish a Telnet session to the device?

This requires a device with ALEOS 4.3.6.011. You can close Telnet with ALEOS software using the AT! QUIT command.

When Reverse Tenet is enabled, can I still connect to the device using Telnet to port 2332?

It is possible to continue using port 2332 to access the device via Telnet, that is,
: Telnet WANIP 2332 will still work.

What is the DB9 pin-out for the AirLink device?

What are the DB9 and RJ 45 Standard pin-outs for Cisco cables?