Heritage Kayaks Heritage Series - Manual (Page 126)

Heritage Series ADSL Bridge/ Router
121 DHCP Server Operation
8.4.1 Network topology
Declarations about network topology include the shared-network and the
subnet declarations. If clients on a subnet are to be assigned addresses
dynamically, a range declaration must appear within the subnet declaration.
For clients with statically assigned addresses, or for installations where
only known clients will be served, each such client must have a
host
declaration. If parameters are to be applied to a group of declarations
which are not related strictly on a per-subnet basis, the
group declaration
can be used.
For every subnet which will be served, and for every subnet to which the
DHCP server is connected, there must be one
subnet declaration, which
informs DHCP of the addresses present on that subnet. A subnet
declaration is required for each subnet even if no addresses will be
dynamically allocated on that subnet.
Some installations have physical networks on which more than one IP
subnet operates. For example, if there is a site-wide requirement that 8-bit
subnet masks be used, but a department with a single physical ethernet
network expands to the point where it has more than 254 nodes, it may be
necessary to run two 8-bit subnets on the same ethernet until such time as a
new physical network can be added. In this case, the
subnet declarations for
these two networks may be enclosed in a shared-network declaration. Some
sites may have departments which have clients on more than one subnet,
but it may be desirable to offer those clients a uniform set of parameters
which are different than what would be offered to clients from other
departments on the same subnet. For clients which will be declared
explicitly with
host declarations, these declarations can be enclosed in a
group declaration along with the parameters which are common to that
department. For clients whose addresses will be dynamically assigned,
there is currently no way to group parameter assignments other than by
network topology. When a client is to be booted, its boot parameters are
determined by first consulting that client’s
host declaration (if any), then
consulting the group declaration (if any) which enclosed that host
declaration, then consulting the subnet declaration for the subnet on which
the client is booting, then consulting the shared-network declaration (if any)
containing that subnet, and finally consulting the top-level parameters
which may be specified outside of any declaration. When DHCP tries to
find a
host declaration for a client, it first looks for a host declaration which
has a fixed-address parameter which matches the subnet or shared network