Subnet change

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Maybe the router. Does the computer get its address via DHCP? If so, the router assigns its address, mask, default router address, and DNS address to use.
 
What mask did it choose? 255.255.255.0 is nice because it is common. This allows 254 addresses on a subnet. I'm wondering if people are getting so many smart devices now that 200+ isn't enough so they expanded your subnet to allow 510 addresses. The number used doesn't really matter as long as it is large enough to do what you need and you use consistent values. But if people enter it manually, they can make a mistake when a 255 becomes a 254 or 252 because it isn't common to them. And then some addresses won't work right if they use the wrong mask.
 
If the device is getting its address from the network server I would not be worried about it. It just doesn't matter to you what the IP address is.

If you need to specify one to get on a different network you can always go in and do that.
 
ptonsparky said:
What would cause the subnet mask of my PC to change?

andnowihavetoputinextracharactersofnonsensetomakethe100characterminimumagain
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Another possibility is that your ISP has upgraded to IPv6. It shouldn't affect your local network though, only the "modem" and router.
 
ptonsparky said:
It changed to 255.255.252.0
I couldn't get to my HMIs.
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My guess is the IT department ran out of addresses so they changed it. They probably don't care about the control network because they don't have to supply addresses to them. You shouldn't worry about it all that much either. Most places the control network is on a separate subnet anyway which is as it should be. You should have to go in and enter a static IP address when you go on the control network unless there is a DHCP server on that network which is not real common.
 
The subnet mask came from the router, and doesn't matter as long as everything on the network has the same setup.

The puzzle is why the router changed.

Did you make any changes on the router? Does the router have an automatic firmware update? How many devices are on your home network?
 
I have multiple computers, two of which have not had any updates lately. I'll see if the subnet on those have changed when I get back later today.

The router is new in the last month. It's a fancy thing designed for homes with a large number of wireless devices. Cameras, switches, etc. I don't have any of those at the moment. Two Roku, a printer, two phones, an iPad. I had no issues with them.

My Internet Provider sold and installed it. The box says it "acts like a router". I don't know enough to make changes to the router. My provider can and guessing it gets auto updates.

Five wired with static IP. Then PCs

Amazing how fast all that adds up.
 
Y'know, 254 addresses (a /24 netmask) goes a long way :LOL: and I don't think I've ever seen a residence need even close to that (maybe I lead a sheltered life). What often gets people is the collusion domains and link saturation. Switches deal with the first and some judicious planning deals with the second (like, don't put all the bandwidth-heavy devices in one part of the house sharing a single link to another part).

It's also amazing how much people overload their wifi.
 
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