Multiple DHCP Scopes for multiple VLANS

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I am using Windows Server 2003 as a DHCP server. I would like to have centralized DHCP management using the one server to give out addresses to each of the 3 VLANS. We are also using Cisco switches and I planned on using the dchp-helper to allow the DHCP packets to be forwareded to the server. I researched online and it seems there is a way to setup the server to give out IP addresses based on the IP address of the switch. Is this the case? If so, how do I configure the Windows 2003 server? I was unable to find any documentation on this. J

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I may be mistaken, but my understanding was the proxy, (whether it is a router running iphelper or a windows DHCP proxy), provides the network it wants the IP for in the request. The main DHCP server responds with an IP from the appropriate scope.

As long as the DHCP proxy knows the subnet the request is coming from, (I assume you are not forwarding broadcasts acroww the router), it should make the proper request.

I suggest you set it up and give it a test.

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    The client issues the DHCP request as a broadcast. The router with IP helper listens for the request and appends its address to the DHCP request and forwards it to the server. The server uses this to determine which scope to offer a lease from. This process changes the DHCP request from a broadcast to a unicast packet, allowing it to travel across the network. The server does not even need to be in the same location as the requesting clients. In my network, we run one DHCP server for a region, serving several hundred sites and 10's of thousand of clients. You do not need to use IP helper on the VLAN that the DHCP server resides on. The broadcast mechanism is sufficient on this VLAN. IP helper can also be used to forward other broadcasts such as WINS. This happens by default. You may need to use ACLs to prevent this if your network is large, and you don't want this on lower speed WAN links.
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  • Skepticals
    astronomer, I wasn't exactly sure about that either. Are you thinking as long as I make three different scopes that are on the same network as each VLAN, the server should issue an IP from the correct pool?
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  • Skepticals
    WANLANman, Perfect. Thanks for your clear and straight-to-the-point answer. I will give it a shot.
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  • Snapper70
    Create all the scopes you would need on the DHCP server. To get client requests TO the server, you have 2 options: 1. On the router linking all the subnets, then on EACH VLAN interface you need IP helper-address [DHCP server on it's native interface]. This will forward the broadcast with a "source network address" which will identify which scope to use. 2. Set up DHCP-relay on a MS server on each of the subnets - it does essentially the same thing. The actual DHCP server doesn't know the difference... (1) is simpler, with no added hardware...
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