A BOOTP relay agent (also known as a forwarder) is an Internet host that passes DHCP messages between DHCP clients and DHCP servers in a subnetted environment. The forwarder usually resides on an IP router; however, any Novell server on a subnet can run the BOOTPFWD.NLM. The DHCP service in Novell DNS/DHCP Services provides relay agent functions as specified in the BOOTP protocol specification (Internet RFC 951).
When a client starts up, it sends a UDP broadcast message, called a Discover packet, to address 0xFFFFFFFF over port 67 requesting an address.
The forwarder has an IP address on the network and acts like a DHCP server, listening for Discover packets from clients on its LAN that are meant for a DHCP server. The forwarder must be configured with the destination address of the actual DHCP server on a different LAN segment that will provide DHCP service.
The DHCP server must be configured to serve the subnet on which the forwarder is located. The DHCP server must have a subnet address range to provide service.
After receiving a Discover packet from a client, the forwarder reformats the packet and sends it to the DHCP server. The DHCP server responds to the forwarder with an Offer packet containing an address for the client.
When the forwarder receives the Offer packet from the DHCP server, the forwarder contacts the client and provides the IP address and lease information.
NOTE: The BOOTP protocol, unlike DHCP, does not provide a mechanism for a client to accept only a single offer of an IP address; therefore, the DNS/DHCP Management Console allows only the server that is specified as the default server in a Subnet object to be assigned to any address ranges that include BOOTP addresses. If you want to assign other servers to the address ranges, you should change the address range type so that it doesn't include BOOTP. If the range type includes BOOTP, you will not be allowed to change the DHCP server assigned to the range.
In environments using a virtual LAN (VLAN), multiple subnets might be defined on one physical subnet. For example, one physical subnet might contain several Class C addresses to form a larger address range than allowed for a Class C address. To accommodate a VLAN environment, a Subnet Pool object must be configured on the DHCP server to bind the multiple subnets together.
If a forwarder forwards client requests from a physical subnet with multiple subnet bindings and these subnets are bound to a single subnet pool, the collection of addresses available in configured subnet address ranges are available to all clients (DHCP or BOOTP) on that physical subnet. This is the primary use of the subnet pool.
Clients that are on the same subnet as the DHCP server do not have to be configured for the subnet pool if the server is bound to all local subnet addresses, or if the server has an address on each local subnet.