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| aznluvsmc 2004-01-13, 9:46 am |
| I'm a little confused on the DHCP service and how it can service multiple subnets. According to my MS Press book, the DHCP server will only assign IP Addresses from a scope that contains IP Addresses which are local to the DHCP server's adapter interface. If that's the case, how can other clients on remote subnets receive an IP Address from the DHCP server when contacting it through a DHCP relay agent or BOOTP capable router? | |
| Mad Jasper 2004-01-13, 2:01 pm |
| In real life, you would include a scope from the subnet you want the DHCP server to service. Example:
Subnet A: 10.0.0.0
Addresses available 10.0.0.2 - 10.0.0.100
Subnet B: 10.0.1.0
Addresses available 10.0.1.2 - 10.0.1.100
You would create this scope on the DHCP server in Subnet A:
10.0.0.2 - 10.0.0.51
10.0.1.2 - 10.0.1.51
Now for a DHCP server on Subnet B you would create this scope:
10.0.0.52 - 10.0.0.100
10.0.1.52 - 10.0.1.100
Now each DHCP server on each subnet can assign IP addresses that span both subnets. This is essential for fault tolerance. Hope this helps. | |
| aznluvsmc 2004-01-13, 4:00 pm |
| So you're saying that each DHCP server would have 2 scopes; one for a the local subnet and one for the remote subnet. If the DHCP server only assigns addresses from the subnet that is local to its NIC's IP address then how does the DHCP server assign IP addresses to a remote subnet? | |
| VOLDAR 2004-01-13, 6:56 pm |
| As you probably already know, if you use one single DHCP server to give IPs to subnets, you have to create a DHCP relay agent in each subnet. This DHCP agent will point to the DHCP server IP address.
A server with DHCP relay agent on the same subnet as the clients can be configured so that it automatically sends all DHCP messages directly to the DHCP server. Included in the message to the server is the address of the originating client so that the DHCP server can respond directly back to the client. This is it. As far as I know of course  - If anyone has another idea, I would love to learn more. | |
| aznluvsmc 2004-01-13, 9:30 pm |
| quote:
Included in the message to the server is the address of the originating client so that the DHCP server can respond directly back to the client.
Actually, the DHCP server does not respond directly to the client since the client does not have an IP address. The DHCP server uses unicast messages to communicate with the Relay Agent. The relay agent then broadcasts the DHCP server's message back to the client. | |
| VOLDAR 2004-01-13, 10:30 pm |
| Okay, you got it. This is exactly what I was saying, in few words, but ... I hope you got the answer you were looking for. 
Good luck with your exam!
check this link DHCP & DHCP relay agent |
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