Specific question on extending subnet on Microsoft DHCP server.

Currently running Server 2012 R2, need to extend on our subnet.  I've found several posts and docs on this, not many touch on adjustments for other devices or servers on the network.

Current IP subnet is 192.168.0.x

I'm looking at following this, will add 255 IP addresses:
https://devget.net/windows/how-to-increase-scope-change-netmask-in-windows-server-2012/

My static IP devices on the network, they will need to have 255.255.254.0 as their subnet mask, correct?  If they aren't updated, they just wouldn't see the second range of IP's at 192.168.1.x?

Routing shouldn't be an issue, correct?  The subnet makes sure the two IP ranges can see each other?

Our firewall IP is 192.168.0.1, any machines that get an IP in the 192.168.1.x subnet wouldn't have issues going out the 192.168.0.1 GW, correct?

Thanks!
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LanMan6401Asked:
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masnrockCommented:
My static IP devices on the network, they will need to have 255.255.254.0 as their subnet mask, correct?
Yes, they need to have their subnet masks updated.

If they aren't updated, they just wouldn't see the second range of IP's at 192.168.1.x?
Well, correct that they wouldn't see the second range. There might be some other communication issues involving communicating to those additional IPs as well, namely exact packets floating because the static systems will have to pass the traffic to the default gateway since they don't understand those IPs are in the same subnet after expansion.

Another approach, depending on how your office space is laid out, would be to utilize VLANs and divide appropriately. For example, you might create a 192.168.1.x VLAN that's in use for one particular floor (assuming you're on multiple floors). Another approach would be that you could have a subnet defined for guest wireless, and another for corporate wireless. These would just be additional subnets, and would prevent you from having to change the mask on the existing.
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Cliff GaliherCommented:
If you change the subnet mask from /24 to /23 (or from 255.255.255.0 to 255.255.254.0 if you prefer that notation) then you are effectively expanding the range of IPs that a device can communicate with.  Don't think of it as having two ranges, and don't use those words. It is just one one single range that happens to be bigger than before. In this instance, terminology matters.  Every device needs to have the same subnet to communicate properly on that subnet. If a device doesn't get updated then it may not see some devices.

Specifically when you say/ask things like this "Routing shouldn't be an issue, correct?  The subnet makes sure the two IP ranges can see each other?"

Routing is not an issue. But they aren't two ranges.  It is one larger range.  Calling them two ranges implies some sort of separation that simply doesn't exist.  It is one big flat subnet.

"Our firewall IP is 192.168.0.1, any machines that get an IP in the 192.168.1.x subnet wouldn't have issues going out the 192.168.0.1 GW, correct?"

You are still treating .0.x and 1.x. as two subnets.  They aren't  It is one *BIG* subnet.  That's why it is called a "subnet mask."  They aren't two subnets. Just one. So yes, as long as the subnet mask tells the machine that .0.1 is in the same subnet as itself, even though it has a 1.x address, it'll reach that gateway just fine.  ONE BIG SUBNET.
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LanMan6401Author Commented:
Thanks Cliff, that really helps.  The more I read, the more I felt myself getting confused. :)
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d0ughb0yPresident / CEOCommented:
Cliff's exactly right. The only thing I'd clarify is that devices with static addresses would have to be changed to use the new mask, because otherwise they will think there are two subnets. They won't send traffic directly to devices in the "other subnet" because they'll think they have to go through a router to do it.
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LanMan6401Author Commented:
Awesome, thank you!
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atlas_shudderedSr. Network EngineerCommented:
Something that I don't see noted in all the responses is that you will need to insure the subnet mask is changed on the firewall interface as well and that any rules that are currently set against the 192.168.0.x/24 range are expanded to the /23 range as well for inclusion of those hosts.
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LanMan6401Author Commented:
This is all the info I'm looking for - thanks Atlas!
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atlas_shudderedSr. Network EngineerCommented:
asker discappeary
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