Question Where is this DHCP IP address coming from?

[JKHill74]

I have a small network operating in a branch office. There are three desktop computers all using wireless, all connected to the same Sonicwall router that serves DHCP.

Two desktop DHCP IPs:
192.168.1.xx
192.168.1.1 (gateway)
192.168.1.1 (dhcp server)

Problem desktop using Intel(R) Dual Band Wireless-AC 8260 - DHCP IPs:
172.16.31.233(Preferred) <- what Ipconfig says
172.16.31.1 (gateway)
172.16.31.1 (dhsp server)

Any suggestions on what might cause this difference? I'd be willing to bet I can disable the Intel 8260 and connect a USB WiFi adapter to solve it but I am curious.

 

[bill001g]

It is generally a unauthorized device on the network. Some brings in a router from home and hooks it up not knowing what they are doing and your whole network goes down.

First look in the ARP table on the machine that has the invalid IP. Since there must be 2 way communication to accept a IP learned via DHCP you should be able to find the mac address of the offending device.

Hopefully the sonic wall has the ability to display the mac addresses it sees on each port. Commercial switches have the ability to display what is called the forwarding table. I can't be sure sonicwall has a command, it must have the table since the mac addresses must pass through it.

If you can ping the gateway from the offending machine just let a ping run and unplug cables until it fails. You then know where the device that gave out the ip is connected.

 

[The Paladin]

Problem desktop using Intel(R) Dual Band Wireless-AC 8260

and you are connecting to your OWN router not a "comcast" free routers or other "free wifi" near you ? because that would explain the address

 

[punkncat]

In theory you shouldn't even be able to see that other computer since it's not within the same IP config/network. I second the above. It is likely connected to the wrong access point.
If you have DHCP set in the router you should be able to set the "get address automatically" setting within the computer adapter.

 

[jsmithepa]

Someone in your home added another WIFI router, or a neighbor's open/no password WIFI router. Do u recognize the SSID?

 

[JKHill74]

and you are connecting to your OWN router not a "comcast" free routers or other "free wifi" near you ? because that would explain the address

The SonicWall was added recently behind a Cox modem/router. This makes me wonder now if the old wireless was not disabled. It's possible there are two wireless routers using the same SSID I suppose. Maybe two of the desktops are accessing one and the third desktop is accessing the second router. ...if that's possible. It would explain a lot actually.