How to assign IP range and DHCP for 400 users ?

Hmm... I'm not as trusting as my fellow responders. 400 workstations at a time? How many total connections? If that were true then the school would be wise to *hire* a company that does this for a living.

If this is a homework question please mention that.

Assuming this is a real-life task, there are probably multiple buildings to deal with, a combination of Wi-Fi and Ethernet, cable stringing and power issues, VLAN considerations, remote access considerations, Internet bandwidth considerations, the list goes on. And we're to assume all of those are worked out, but you have a little question on which subnet mask to use and how to change the DHCP server.

The IP scheme you use should be well-thought out *before* implementing it. Should each building or classroom use a slightly different range to help diagnose issues and play nice with the switches? Or group them by category (Math, Science, Languages, etc.)? Or just one hellacious subnet, assuming your backbone equipment can handle 400 IPs?

I wish you well, but I'm still not convinced.

Internet connection is not the real problem here as providing 400 client connections in a network to a single ISP connection is fairly straight forward. You will need a fairly fast ISP connection if the client users are to have a reasonable Internet speed.

What will be a potential issue is if every client computer is to be able to use Microsoft networking to every other client. If the clients can be logically grouped with different groups not interworking directly, and each group is limited to perhaps only 50 clients, then normal domestic style routers and switches could be used.

A different approach would be to implement a client server architecture where all the main processing is performed on a small number (perhaps 8) multi-user servers, and with low cost low performance PCs providing the user front end screens, keyboards and mice. This approach means that the client machines never need to communicate with each other as all communication between users is performed within the small number of central servers.

A client server architecture has the advantage that it is relatively easy to update a small number of servers so they all have compatible software rather than updating 400 client machines. Backups can be handled centrally so everybody's data is secured. Implementing a help desk working with the small number of servers is much more efficient than have helpers running round the building. If a user's computer fails, simply drop in a different computer and when the user logs in they have all their work immediately available.

You could go for a single network with a full capability PC for each user. The network would require a mask of 255.255.254.0 to give a total of 510 usable addresses. You would need a commercial style DHCP server, probably implemented in a PC based server rather than within a router. Addresses can be derived from any of the private address ranges such as:

192.168.0.0 to 192.168.1.255

or 172.16.0.0 to 172.16.1.255

or 10.0.0.0 to 10.0.1.255

or any of the other address ranges in each of the private address ranges.

I hope this helps.

This is far beyond the capacity of a regular router.

Things to clarify:

- Do these users interact directly together or mainly access the Internet?

- How many wired and wireless connections do you need?

- How big is the area to cover with wifi?

Once those questions are clarified and you can make a plan of the different devices you need for the whole setup, you should arrange the subnets based on the physical installation.

Note that I have a hard time understanding how you deploy users like that though.

This is done regularly on enterprise equipment, not home routers.

You design the scope and network for the max number of users at any one time.

There are 2 ways to allow the DHCP server respond. One is to have a trunked interface connected to your DHCP server and allow it to "listen" to DHCP requests on all the VLANs you want DHCP. This requires VLANs.

The other easier way is to just use dhcp helper address on your router. This "forwards" the dhcp request to a central dhcp server, and that server knows from the forwarding ip which scope to use. The request does come back as a DHCP packet so if you have ACLs or firewalls they must allow the packet back. This is the standard way of deploying DHCP in a routed environment. Most routers/manufacturers support this function.

First question, what DHCP server are you using? Can't really answer your configuration question without that.

If you want a single subnet, then a /23 (subnet mask of 255.255.254.0) would work. If you don't understand that you need to learn subnetting first.