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mark_D74Flag for Ireland

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Change subnet - effects on server

Hi,
Our school network has the following:
Sonicwall NSA 250 M Router (acts as gateway and also handles a separate VLAN)
Network address  192.168.1.0 / 24 (subnet mask 255.255.255.0)
Single DC running Server 2016 std (ip 192.168.1.50), handling DNS and DHCP
About 150 endpoints

We're in danger of running out of IPs, so I'm hoping there's a way we can change just the subnet mask and retain the 192.168.1.1 - 192.168.1.254 range while gaining an extra range of IPs on the same, new subnet (for example 192.168.2.x, or .0.x) .  I'm also hoping that changing the subnet mask (but not the IP) of the DC will not cause problems. I know I'll have to reconfigure the subnet mask on any non-dhcp devices (such as network printers and the server).

So I've a couple of questions. What's the best way of doing this?  
Which subnet mask would yield what ranges of IPs?  
Is changing the subnet likely to cause any issues for the server (which I envisage keeping on the same IP?

Thanks in advance.
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Seth Simmons
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that's what i would do...change the mask to 255.255.254.0
that will yield another 254 addresses
shouldn't cause any issues; it just allows the system to access that additional range (192.168.1.0 - 192.168.2.254)
With you current subnet you still have 54 IP to give out and that is assuming that all IP's below 50 are being used.

 If you are close to 254 IP's that is a different story.
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Chris Dent
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As mentioned, you could go for the subnet mask change to double your subnet size. Another option would be to create another VLAN and allow communication with the existing one (you might decide you want to have VLANs for particular sections of the school in order to keep the broadcast domains smaller).
You can reconfigure the subnet mask as the below :
first net 192.168.1.0 (192.168.1.1 - 192.168.2.254) = 510 hosts in one network with prefix /23 or 255.255.254.0 but you may face a too much broadcast storm .
As stated above, with a subnet mask of 255.255.254.0 the boundary is 192.168.0.0 to 192.168.1.255, not 1.0 to 2.255. You don't get a choice about the boundary, it's a result of binary math.
How is the school laid out? I'd go with VLANs by section of the campus, along with VLANs that have specialized purposes (i.e. security, wireless, VoIP, etc). Allowing inter-VLAN communication is easy.
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Thanks for the advice guys - can anyone advise whether changing the subnet will have any effect on the Windows server?  It has a static IP, which can remain the same, but I presume I'd have to enter the new subnet mask.
No real effect, the change is a small one really.
As long as things are done correctly, not really. Some slowdown (generally a small amount)  might occur if you have a lot of network broadcasts occurring (more prone to occur if you have a lot of Apple devices).
A change in subnet mask does not automatically mean you have more broadcast traffic. Something has to send the traffic, you need more hosts for that. It does mean you have more potential, because the size of the broadcast domain is greater, but it's potential.
Thanks. So the server doesn't mind having a different subnet mask entered on it's LAN interface - I thought it might raise an objection by refusing to work.  I presume only more live hosts would create more broadcast traffic, not simply having larger potential IP scope.
It should be fine with the change. Because you're using 1.x at the moment the directed broadcast (192.168.1.255) won't even change.

You will, obviously, need a consistent subnet mask if hosts within 192.168.0.x are to communicate with those in 192.168.1.x.
Thanks for all the help everyone!