WiFi Strange network IP issue

[Bk456]

A friend asked me to look at his broadband. It is not working at times every day

Standard internal IP format is 192.168.1.x

But the IP address for said device is changing to 192.168.0.x. The default gateway is also getting replaced with a zero but subnet masks remains 255.255.255.0.

Phoned BT but they can’t see a fault anywhere nor could the girl even give any input to the problem. She said it’s normal for IPs to change. I agreed but said the 1 in the third segment should never change.

Anyway the hub was ran over a 10m extension dsl cable. It’s homehub6. I’ve put it back in the Hall with standard short dsl cable. I’ve reset the hub then set a custom SDID and new password and also set the PC to run a wired connection so he can test for a few days and see if it’s fixed or only WiFi was affected.

All devices in the house affects btw, desktop, iPad, galaxy, iPhone etc. On the iPhone you can actually see the ip info change

Has anyone seen this issue before?

 

[JonMMM]

BT woman does not know what she is talking about. It is normal for you WAN to change every so often and it is possible for your LAN clients to change but to change from 192.168.1.x to 192.168.0.x means that the default gateway has changed which really is not possible. The long telephone lead should not be the issue. Has he changed ISPs? has he ever used the neighbours wifi, it sound to me like at some point he has connected to another wifi signal and for wome reason it is trying to reconnect to that signal.

When the IP changes can does the router address change too?

 

[Spectre]

What happens if you configure static IP addresses? It sounds like a DHCP server (probably the router) is issuing IP addresses on a different subnet to the gateway.

I'd look at the router settings a bit more and try disabling DHCP to test.

Check the scope of the IP addresses it can issue.

 

[jfish]

seen this happen before, looks like another DHCP server is on the same network or peice of wire. With DHCP being UDP (not TCP) so when a client sends out a DHCP packet, the first DHCP server to reply which dish out IP address, hence the way the IP changes from one subnet to another.

the subnet mask will remain the same, as the 192.168.x.x is a class C private network and also non routable (in sense of on the tinternet - and NAT is used to route your packet from your private IP to public IP)

 

[Bk456]

There was a tp link booster in the hall. I unplugged this just in case this was interfering with things

 

[jokejong]

i think the tp-link device is running a dhcp server and providing ip address in the 192.168.0.* subnet. Login into the device via web, and disable dhcp services. do remember to label the device with the IP address and username and password info so that one can always login again in future.

it'll be good to change the default IP address from its original 192.168.0.1 or 192.168.0.254 to the 192.168.1.* addresses, and please set the IP address to an address that is outside of the 192.168.1.* DHCP scope/range.

 

[kevshed]

Agree with the earlier posts - devices can't dynamically change IP Range - i'd be pretty sure there is another DHCP Server there somewhere, and its renewing from the wrong server from time to time. What you could do - going static would solve it, but i'd still be concerned that if something else is issueing addresses, other devices will fall foul to the same thing.

 

[woakme10]

Put in a static IP address that belongs to your networks and it should retain it.

 

[majo72]

You have two different DHCP-servers in the same network for sure. Perhaps you have a DSL modem and router connected in parallel? They should be serially connected DSLModem LAN->Router WAN->Router LAN->clients. Nothing else.
Both DSL modem as well as the router distributes dynamic IP:s (one at 192.168.0.x and the other 192.168.1.x). Whatever the client reaches first handles the IP to the client.