From: John Cuccia 

>One server can handle multiple subnets if the routers connecting those
>NICs are configured to forward DHCP broadcasts to the subnet on which
>the DHCP server is located.

Sorry, the above should read,

"One server with a single NIC can handle multiple subnets if the
routers connecting those subnets are configured to, etc, etc."

>Configure the DHCP server with a scope
>for each subnet for which it will be supplying addresses.


>
>The Cisco config directive is "IP Helper-Address x.x.x.x":
>
>http://www.cisco.com/univercd/cc/td/doc/product/software/ssr83/rpc_r/48383.htm
#xtocid670625
>Excerpt:
>There are circumstances in which you want to control which broadcast
>packets and which protocols are forwarded. You do this with helper
>addresses and the forward-protocol commands.
>
>The ip helper-address interface subcommand tells the router to forward
>UDP broadcasts, including BootP, received on this interface. (UDP is
>the connectionless alternative to TCP at the Transport Layer.) Use the
>ip helper-address interface subcommand to specify the destination
>address for forwarding broadcast packets. Full command syntax follows.
>
>ip helper-address address
>no ip helper-address address
>The address argument specifies a destination broadcast or host address
>to be used when forwarding such datagrams. You can have more than one
>helper address per interface. You remove the list with no ip
>helper-address.
>
>If you do not specify a helper address command, the router will not
>forward UDP
>broadcasts.
>
>Example:
>This example defines an address that act as a helper address.
>
>ip helper-address 121.24.43.2
>
>
>
>The ip forward-protocol global configuration command allows you to
>specify which protocols and ports the router will forward. Its full
>syntax is listed next.
>
>ip forward-protocol {udp|nd|spanning-tree} [port]
>no ip forward-protocol {udp|nd|spanning-tree} [port]
>
>The keyword nd is the ND protocol used by older diskless SUN
>workstations. The keyword udp is the UDP protocol. A UDP destination
>port can be specified to control which UDP services are forwarded. By
>default both UDP and ND forwarding are enabled if a helper address has
>been defined for an interface. If no ports are specified, these
>datagrams are forwarded, by default:
>
>Trivial File Transfer (TFTP)
>Domain Name System
>IEN-116 Name Server
>Time service
>NetBios Name Server
>NetBios Datagram Server
>Boot Protocol (BootP) client and server datagrams
>TACACS service
>
>Use the no ip forward-protocol command with the appropriate keyword
>and argument to remove the protocol.
>
>Example:
>The example below first defines a helper address, then uses the ip
>forward-protocol command to specify forwarding of UDP only.
>
>interface ethernet 1
>ip helper-address 131.120.1.0
>ip forward-protocol udp
>

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