HP 200 Series Services And Applications page 141

Internet Protocol Routing Service
BootP and DHCP
All-Networks or All-Subnets Broadcast Address
is 255.255.255.255, the default used when there are no addresses config-
ured in the Bootrequest destination list. An all-subnets broadcast
address has the network number followed by all zeroes or all ones. For
example, a network 15 all-subnets broadcast is 15.255.255.255. The class
B network number 128.1 has an all-subnets broadcast of 128.1.255.255.
There are two cases to consider: either the relay agent has an interface in
the specified network, or the relay agent does not have an interface in the
specified network. If the router has one or more interfaces in the specified
network, it transmits a Bootrequest packet on each adjacent subnet with the
specified network number. The destination IP address of each packet is the
all-hosts broadcast address for the subnet on which the packet is sent (for
example, 15.1.1.255). Since the packets are addressed only to the adjacent
subnet, all routers in the path between the client and server must have
Bootp relay agent functionality. For the second case, routers that are not
relay agents drop the Bootrequest packets. The other relay agents relay the
Bootrequest packets in accordance with their configured destination
address lists.
If the router does not have an adjacent subnet in the specified network, it
will forward the Bootrequest along the path to the destination network as
learned by the routing protocol. Thus,, no relay agents are needed between
the relay agent that initiated the Bootrequest and the first router with an
interface in the destination network. The first router that has an interface in
the destination network must be a relay agent. It forwards the Bootrequest
in accordance with its configured destination address list.
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