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We have a laptop with intermittent wifi connectivity problems. Rebooting often helps.

Today while digging around I noticed that its DHCP IP address and gateway are not addresses on our subnet. The DCHP lease it's using hasn't expired but based on the timestamps it was probably obtained while on a different network with a different SSID. For some reason the laptop is trying to use that DHCP lease on our network but has no connectivity because the gateway doesn't match.

I suspect if I do a ipconfig /release it will get a new IP address correctly, but I want to know why it's trying to use a lease from a different DHCP server.

Is this a misconfiguration on the laptop somehow? Or a problem with our office DHCP server?

Edit with more info:

Our company wifi network has a non-generic SSID and a subnet of 192.168.1.0/24. The DHCP and gateway are both on that subnet. Wifi access points are set to "bridge" mode (our Windows domain controllers do DHCP for the LAN including Wifi).

The user of the laptop came in today saying he had been using the laptop at a client's office that morning (don't know the SSID but I can pretty well guarantee it wasn't the same as ours).

The laptop connects to our wifi network but gives a "no connectivity" error and has no access.

ipconfig /all reveals that the wireless card has a DHCP-assigned IP address of 192.168.99.102 and a gateway of 192.168.99.1. Not our network! The lease was issued that morning, presumably by the client's network, and is still valid. But obviously it's the wrong network.

Edit 2: The Plot Thickens

We disconnected from the company wifi and connected to a different one, and the laptop works. It's given an IP address of 10.0.0.45 (different network, different DHCP range). Wifi works fine.

When we bring it back onto the company network it doesn't work again, but this time ipconfig /all shows that it's holding onto the 10.0.0.45 IP address!!

So something about that laptop or our DHCP server is causing the laptop to just use a random old DHCP lease when connecting.

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A DHCP client will attempt to use the same ip address unless it hears otherwise from the DHCP server while booting. Does the existing DHCP assigned ip address match your subnet? –  joeqwerty Nov 12 '13 at 19:26
    
No, the DHCP-assigned address it's using is on a random subnet -- not one of ours, and the IP address does not appear in our DHCP lease table. The gateway IP address is also not ours. The laptop seems to be continuing to use a DHCP lease from a completely unrelated network. –  Henry Jackson Nov 12 '13 at 19:51
    
Is the gateway it gets yours or the other subnets? Can the client ping that gateway or the DHCP server IP it got it from? –  TheCleaner Nov 12 '13 at 20:01
    
You need to find out where the laptop got its ip and gateway from. Could it be another network with the same SSID or is your SSID unique enough (not something generic like Linksys or Netgear)? And does this occur during the day (while it should be connected to your SSID) or always when it comes new to your network? –  Rik Nov 12 '13 at 20:26
    
@TheCleaner: Added some more info to the question. –  Henry Jackson Nov 12 '13 at 23:52

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