Question Devices connecting via DHCP to unknown range of addresses ?

[robburne]

I am running a Linksys MX4000 router, all has been working fine until some recent strange behaviour. I noticed that some laptops and my firestick had no connectivity. When I check the settings for each device they are connected to the correct SSID but they are connected on the range 192.168.1.x - my network is configured to use 192.168.0.x with corresponding DHCP also configured to use a range of this:

There is only one router transmitting the SSID which the devices are connected to so how or why are they connecting using the incorrect address range?

I've tried the "forget" wifi network on the concerned devices, rebooting and then re-entering wifi passwords but they just reconnect to the wrong range again. I should note that I do also have devices connected via DHCP and are assigned address from the correct range.

I am really confused and don't know what else to try. Any ideas?

Thanks.

 

[bill001g]

You likely have another router or at least a device that has the dhcp server function in your house.

I would start by turn off your router wifi radio, you could just turn off the router if you can't find the wifi settings. This is to be really sure you are connected to the wifi signal you think you are. Years ago when routers came with the same ssid and default passwords it was easy to connect to a neighbors wifi.
Your devices should all not be connected. This should also clear all the IP information hopefully.

If you do IPCONFIG /all on the laptop that has the wrong IP I assume you see the DHCP server and the gateway IP of 192.168.1.1.

Can you ping that IP. If it will ping I would then try to turn other devices off and see if you can make it go away.

If you do ARP -a you should see the mac address of the device. Not sure if that will give you any clue but sometime it does.

Although this is mostly caused by a router you sometime get stuff like controllers for security cameras or other so called "smart" devices that do this.

 

[Ralston18]

@robburne

The following links may help indentify a device via a discovered MAC:

https://macvendors.com/

https://dnschecker.org/mac-lookup.php

There are other similar links to be found.

You should not have to provide any information beyond the MAC address being researched.

Nor should you need to download and install anything.

Leave any website that wants to or attempts to do more.

Be aware that the website results may not be fully accurate as companies come, go, merge, etc. - name changes, etc..

Some MAC addresses may be being reused anyway....

 

[robburne]

The SSID is 100% unique, it is the name of my ISP followed by a AAhyphen and then 4 random digits. Just to be sure I switched the router off and sure enough the network was not found and the devices would not connect.

I left the router off for a few minutes and upon restart my devices are now connecting to the correct address range. So I'm wondering, could the DHCP server have exhausted all possible address and could it have perhaps then move from 192.168.0.x to 192.168.0.x, and in doing a hard reboot the DHCP has been reset my firestick for example is connected at 105, the address range starts at 100.

 

[bill001g]

The DHCP server function in a consumer router is very basic. It would just stop giving out IP if it ran out. It also would not give a different gateway IP they always give out their own IP.
For some period of time you likely had a second DHCP server on the network. Hard to know exactly. It is key to try to get the mac address when this happens so you can know to a point which device caused it.

This is actually extremely common issue in business. Some stupid employee decides something is not good enough with network near their desk. They bring in a home router and plug it into the network using the default out of the box config. This simple function can kill a huge network. Commercial switches have features that prevent DHCP servers from being added to a network.