Need some advice on using a single dhcp for multiple subnets

[ImanVajdi]

Hi Guys,

I'm working on a project for uni and i was woundering if i can get some advice from you guys.

The Senarion (in a nutshell):

ABCD is a company with 4 offices (A, B, C, and D). They require a company network to connect those offices and provide other services plus they want the network to be as secure as possible.

Each office wihtin the company is to be on its own Class B subnet with at least 30 hosts per office. All offices are to have dynamically allocated IP address using DHCP.

Using these equipments ( various cisco routers, 20 PC's and couple of switches ) you produce a prototype network.
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There loads more requirements but I have found the soloutions for them already my problem is the solution for the dhcp.

What I've been trying to do is to setup a single dhcp server to handle the IP allocation for all the subnets and so far I have found out that to do that I need to use the ip helper command but that would require at least four ethernet ports on the router which as far as i know normaly routers don't have.

So Ithink the other soloution would be adding a router for each subnet which I don't think is very cost efficent (5 routers in total for a network with only 120 nods!).

Now I'm not sure what's the best way to sort out the dhcp problem, I need to find a way to make sure dhcp allocates the right range of IP's to the right office. For example Subnet B's range should be allocated to clients in office B.

I've been reading everything I could find for past couple of days but I'm not sure what's the best sloution, so if you could give me some advice will really appreciate it.

Thanks
Iman

[coopstah13]

a router can work with only 2 ports, one external and one internal, the internal can be connected to switches which in turn can be connected, so you can have any number of ports

[ImanVajdi]

Thanks but if you read my post a bit more carefully you'll see that I already know how many ports a router or a switch got !

My issue is that I don't know how to seprate my subnets, or in other words how can I make the dhcp understand to send the Subnet A's IP range to subnet A clients and not clients on subnet B without seprating the subnets via routers and then using IP helper command.

I don't have problem with the practical part of it, I just want to make sure that I'm getting the design right.

Many Thanks
Iman

[HROAdmin26]

Depending on the class of router, multiple ports for multiple networks is common - but the price goes up quickly.

Managing multiple networks with one interface is usually done with VLAN's and trunking. DHCP broadcasts are (normally) only sent to the local subnet. If your DHCP server (Linux) is only on one network, it cannot receive requests for non-local networks. This is where 802.1q trunking comes in. If your DHCP server is a Cisco device, IOS has an option to forward DHCP requests from the local subnet to some other system.

Since this appears to be a homework question, I suggest doing more Google searches.