User`s guide

298 XSR User’s Guide
DHCP Services Chapter 12
Configuring DHCP
DHCP Services
The DHCP services comprising the Bindings Database, leases, network
options, and Client Class configuration are described below.
Persistent Storage of Network Parameters for Clients
The first DHCP service is persistent storage of network parameters for
network clients, also known as the bindings database. The XSR directs the
Server to store a [key:value] entry for each client, where the key is some unique
identifier and the value contains configuration parameters for the client.
For example, the key might be the IP-subnet-number/hardware-address pair.
Alternately, the key might be the IP-subnet-number/hostname pair, allowing the
server to assign parameters intelligently to a DHCP client that has been
moved to a different subnet or has changed hardware addresses. DHCP
defines the key to be IP-subnet-number/hardware-address unless the client
explicitly supplies an identifier using the client identifier option. The XSR
stores host IP and client-hardware addresses, intervals, client-identifiers, and
client-names in the
leases.cfg file.
Temporary or Permanent Network Address Allocation
The second DHCP service is temporary or permanent network (IP) address
allocation to clients. Network addresses are dynamically allocated simply by
a client requesting an address for an interval with the server guaranteeing not
to reallocate that address within the requested time and attempting to return
the same network address each time the client requests an address.
Lease
The period over which a network address is allocated to a client is called a
lease. A client may extend its lease with follow-up requests and may issue a
message to release the address back to the server when the address is no
longer needed. Also, a client may request a permanent assignment by asking
for an infinite lease. Even if it assigns permanent addresses, a server may
distribute lengthy but non-infinite leases to allow detection of a retired client.
In some environments network addresses must be reassigned due to the
exhaustion of available addresses. In this case, the allocation mechanism will
reuse addresses whose leases have expired. The server will use any available
data in the configuration data repository to choose an address for reuse.