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I have a RUT240 modem serving WiFi to a laptop. Under normal conditions, the laptop gets a 192.168.1.x IP address, which is what I configured. Life is good.

The RUT240 modem is connected to mobile (sim card, LTE) and to WAN (ethernet connection).

Sometimes when I reboot the RUT240, by removing the external power and NOT by using the Web UI, the laptop gets an IP address in a range that is NOT 192.168.1.x, but in the range of the EXTERNAL WAN connection. This is as if the router is acting in bridge mode for some unknown reason. It can be there for 30 minutes or so.

In this scenario I have no way of loading the UI of the rut modem since it is configured to listen on the inside network and surely enough 192.168.1.1 does not work anymore.

I reboot the RUT240 several times and then it comes back to normal: the laptop gets an IP in the 192.168.1.x range, I can open the UI and life is good again.

What can be going on here?

Some observations below.

ipconfig of the laptop when it has a "normal" IP address:

Wireless LAN adapter Wi-Fi 2:

   Connection-specific DNS Suffix  . : lan

   Link-local IPv6 Address . . . . . : fe80::810:c5fe:df5d:70e%17

   IPv4 Address. . . . . . . . . . . : 192.168.1.234

   Subnet Mask . . . . . . . . . . . : 255.255.255.0

   Default Gateway . . . . . . . . . : 192.168.1.1

ipconfig of the laptop when the rut240 is "Acting up":

Wireless LAN adapter Wi-Fi 2:

   Connection-specific DNS Suffix  . : somecorp.com

   Link-local IPv6 Address . . . . . : fe80::810:c5fe:df5d:70e%17

   IPv4 Address. . . . . . . . . . . : 192.168.216.36

   Subnet Mask . . . . . . . . . . . : 255.255.255.0

   Default Gateway . . . . . . . . . : 192.168.216.1

somecorp.com is the name of the corporate network where the router is connected via ethernet, its WAN interface.

If I connect the laptop to this corporate network directly via ethernet (no modem involved) the laptop gets an IP address in that range (192.168.216.x) with an identical C.S. DNS Suffix.

What could be going on here?

I have NOT configured the router to become a bridge (as far as I know).

Thanks!

PS: removing the power is a robustness test of this setup.

1 Answer

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Hello,

This is some interesting behavior.

In such an instance, I would like you to try the following. Set your wireless interface with a static IP by going to Wi-Fi properties -> Internet Protocol Version 4 and selecting Use the following IP address. Set the IP from the pool of 192.168.1.100 - 192.168.1.249 and set default gateway as router's LAN IP address 192.168.1.1. This should allow to access the device's WebUI. 

I would then like you to generate a troubleshoot file by going to System -> Administration -> Troubleshoot section and downloading the file from there. Attach this file by editing your question. It will provide information about the router's configuration.

In case that is not possible, please try resetting the device to factory defaults by holding the reset button pressed between 12 - 20 seconds and see if it happens again.

Also, what firmware version is the router currently running?

Have you made any additional configuration changes?

Best regards,