User`s guide

300 XSR User’s Guide
DHCP Services Chapter 12
Configuring DHCP
Nested Scopes: IP Pool Subsets
As mentioned earlier, one of the main functions of the DHCP Server is to
allocate IP addresses to clients. In that process, the DHCP Server works with
three scopes or resource sets responsible for aggregated DHCP attributes -
Pools or subnets, Client Classes, and Hosts. Scopes can be assigned other
attributes as well as IP addresses, and can nest these attributes hierarchically
much like files are organized in a directory tree. How these scopes interrelate
can be loosely illustrated as shown in Figure 52.
Figure 52 DHCP Nested Scopes
The Pool scope in Figure 52 defines and manipulates IP addresses and
parameters. The Client Class scope manages sets of clients requesting DHCP
Server services. The Host scope controls DHCP user parameters.
When the DHCP Server surveys its clients by using the manual bindings of a
client-identifier or hardware-address, and host address, it generally inherits
attributes from an outer scope down to an inner scope. But, the DHCP Server
will override outermost attributes when they are found first at the Host scope.
For instance, if a
domain-name is specified for lcurtis-xp in the Host scope and
another domain-name in the Pool scope for all clients on the 192.168.57.0
network, the DHCP Server will always select the Host scope attribute.
Pool (subnet)
Client Class
Host
Values are inherited
from outer scopes
A nested scope may
override an outer
scope attribute
Attributes persist
at the Host level
Values are inherited
from outer scopes
192.168.57.0
lcurtis-xp
Elite
Pool (subnet)
192.168.57.0