Expanding IP range on DHCP server for 800+ devices

We are expanding the internet access to the entire school body and we will need 800+ ip addresses to accommodate them all. the existing DHCP range is 192.168.1.0 with a Mask of 255.255.255.0 the default Gateway is at 192.168.1.254. if i open the mask to 255.255.248.0 it moves it to a class B network, so does that mean i have to change my existing ip address range from 192.168.x.x to a class B range? If i set the range from 192.168.1.0 to 192.168.7.255 using subnet mask of 255.255.248.0 I will have to move the Default Gateway from 192.168.1.254 to something outside the range. i tried to start the rang at 192.168.2.1 to keep the DFGW at 192.168.1.254 but i get an error saying the gateway is not on the correct subnet? Is there a better way to do this?

Thank you
mspencer100Asked:
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masnrockCommented:
if i open the mask to 255.255.248.0 it moves it to a class B network, so does that mean i have to change my existing ip address range from 192.168.x.x to a class B range?
If by that you mean whether you need to update the subnet mask on existing devices, then yes. You definitely will need to figure out how you want to have your DHCP scopes working.

If i set the range from 192.168.1.0 to 192.168.7.255 using subnet mask of 255.255.248.0 I will have to move the Default Gateway from 192.168.1.254 to something outside the range.
You don't *have* to, but you do need to be sure that the gateway address stays out of the DHCP range.

How is the school laid out? VLANs may make more sense. You might have VLANs by floor, by type (wired, wireless, security devices, etc). It adds complexity, but also introduces better organization if done correctly.
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mspencer100Author Commented:
i guess the question is do i have to change the IP address to a proper Class B address 172.x.x.x or can i keep the 192.168.1.x  range if i change the subnet mask to 255.255.248.0?
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Peter HutchisonSenior Network Systems SpecialistCommented:
You can convert to a Class B range (ie 172.16.0.0/12 ) or go fully to a Class A range (10.0.0.0/8). As masnrock says, switching to proper VLANs would make sense in a medium to large organisation.

See articles
https://technet.microsoft.com/en-us/library/cc958825.aspx 
https://support.microsoft.com/en-us/help/255999/increasing-the-number-of-ip-addresses-on-a-subnet-in-dhcp-server
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masnrockCommented:
You can use 192.168.1.0/21 without issue. Bear in mind that the 192.168.0.0/16 is an entire range of private IPs. While you don't have to utilize the entire thing, you certainly have a lot of room to expand in it.
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gilnovSystems AdministratorCommented:
Just to expand on masnrock's points, the gateway has to be on the same SUBNET with your clients or they won't be able to reach it. The whole idea of moving it out of the scope is to avoid an address conflict between the clients and the gateway which would turn the universe inside out...well...your network anyway. You could do it with an address reservation in your DHCP scope but it's a better (best?) practice to just keep the gateway address out of the DHCP scope altogether. The magic of DHCP is that all your clients will get the new settings automatically with a reboot...unless you have the gateway defined statically on every client. Please, man! Tell us you don't have the gateway address statically assigned on all you clients!!!
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8046586Commented:
Best practise is using a VLAN, but that requires appropriate hardware. I think you should not improvise because the last thing you want is a network as a bottleneck in the system.
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
To clarify and summarize:
It is absolutely no issue to have the gatewy inside of your DHCP pool. There is no need to change the gateway. You create a reservation, or just exclude its IP from the DHCP pool.
There is also no need to change the IP address, as has been said correctly above. The important point is that indeed 192.168.0.0/16 is reserved for private use, and you can create subnets within that as you need.
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Tom CieslikIT EngineerCommented:
You did not mentioned what kind of hardware you have and if DHCP is on router/firewall or some Server.

If you can consider server based DHCP the simplest way is to create multiscope.
This will require to have a firewall with 4 LAN connections that you can assign as a gateways for each scope in superscope, but it's very easy to set and is working very good.
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masnrockCommented:
While this question has been abandoned, the OP's question has certainly been answered (even though it isn't known what approach was taken at the end of the day).
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
#a42416997    correct answer
#a42417009    correct and important expansion on that answer
#a42417064    is summarizing both, and might receive some points (or not)

I recommend an equal split between the first two comments listed.
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