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client used a client ID when it got the lease, it will use the same identifier in the message.
Alternately, when a lease is near expiration, the client tries to renew it. If unsuccessful in
renewing by a certain period, the client enters a rebinding state and sends a DISCOVER
message to restart the process.
DHCP also sets various options/extensions to clients which are outlined in
Configuration Values to Clients: Options"
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
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 exhaustion of available
addresses in which case the allocator reuses addresses whose leases have expired. The server will
use any available data in the configuration data repository to choose an address for reuse.
For example, the server may choose the least recently assigned address. As a consistency check,
the allocating server will also probe the reused address before allocating the address - e.g., with an
ICMP echo request - and the client will also probe the newly received address - e.g., with ARP.
Assigned Network Configuration Values to Clients: Options
With the exception of IP address assignment to clients, the DHCP Server provides a framework
for passing configuration data to hosts on a TCP/IP network. Configuration values and other
on page 15-3.
leases.cfg
DHCP Services
"Assigned Network
file.
XSR User's Guide 15-3
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Troubleshooting
