I work at a university and something strange is happening: sometimes, people in my department lose internet connectivity. When I check the adapter properties (IPV4), I notice that the subnet mask has changed itself!
We use the format 255.255.255.0 regularly and the change is always to 255.255.0.0. This appears to happen after Windows updates much of the time, but occasionally happens after a user turns their computer on.
Regrettably, I don't have access to any of the servers...they are controlled by our IT department and they won't let us anywhere near them (which is a good thing as I don't know enough to be using them!).
I'm guessing I won't be able to solve the problem and will have to just correct the subnet mask every time it changes on us...oh well, could be worse!
We are using static IPs...when the subnet mask changes we have to go into the IPV4 properties menu and change the subnet mask back to 255.255.255.0.
Interestingly, another issue has been noticed: we are also losing the DNS server entry on the IPV4 properties menu! A few people had lost their Internet connection and I thought it would be the subnet mask issue...when checking the IPV4 settings I noticed that the DNS server had been erased! This happened on several different machines.
As previous commenters have mentioned, likely there is a setting on a server that needs attention. Regrettably, I do not have access to the servers and I wouldn't even know what to do if I could access them! I have a feeling we may just have to live with this problem for now!
If you are not using DHCP, nothing on your server should be changing the settings. Is this happening to the same computers all the time?
Yes, for the most part it seems to be the same computers with the issues.
The person who recently had their DNS automatically erased did not suffer from the 'changing subnet mask' issue...I'm wondering if the affected people are using some type of software that is causing trouble with their network settings.