Technical data

Configuring the DHCP Server
7.1 Key Concepts
Table 7–1 DHCP IP Address Allocation Methods
Method
Applicable
Client Description
Dynamic DHCP and
BOOTP
The DHCP server assigns an IP address from an address pool
to a client for a specified amount of time (or until the client
explicitly relinquishes the address). Addresses no longer
needed by clients can be reused.
Use dynamic allocation when:
• Clients plan to be connected to the network only
temporarily.
• You have a limited pool of IP addresses that must be
shared among clients that do not need permanent IP
addresses.
• IP addresses are scarce, and you need to reclaim retired
addresses so you can assign them the new clients being
permanently connected to the network.
For BOOTP clients, DHCP assigns dynamic IP addresses
from the address pool and stores the addresses in the lease
database by assigning each lease a time of infinity.
Static DHCP and
BOOTP
The system manager manually assigns (in the DHCPCAP.
file) an IP address to a client and uses DHCP to pass the
assigned address to the client.
Use static allocation in an error-prone environment where it
is desirable to manage IP address assignment outside of the
DHCP functionality.
Finite BOOTP-only The DHCP server assigns an IP address from the pool to
the BOOTP client and defines a lease time based on certain
parameters you define in the SERVER.PCY file. When the
lease expires, the DHCP server pings the IP address. If the
server receives a reply, it extends the lease and does not offer
the address to a new client. If not, the address is free and can
be assigned to a new client.
Section 7.5 explains how to configure the different types of addressing for clients
on your network.
The typical network uses a combination of static and dynamic DHCP addressing.
As the local system manager or network administrator, you can apply any of the
IP addressing methods as appropriate for your specific policies and environment.
7.1.3 Relationship Between DHCP and BOOTP
From the client’s perspective, DHCP is an extension of the BOOTP functionality.
DHCP allows existing BOOTP clients to operate with DHCP servers without
having to change the client’s initialization software.
Based on the format of BOOTP messages, the DHCP message format does the
following:
• Captures the BOOTP relay agents and eliminates the need to have a DHCP
server on each physical network segment.
• Allows existing BOOTP clients to operate with DHCP servers.
Configuring the DHCP Server 7–3