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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)            9  Host Configuration and TCP/IP Host Configuration Protocols (BOOTP and DHCP)                 9  TCP/IP Dynamic Host Configuration Protocol (DHCP)                      9  DHCP Client/Server Implementation, Features and Issues

DHCP Client/Server Implementation, Features and Issues 1 2 3 DHCP Client General Implementation and Management Issues

DHCP Server Software Features

In most networks you will choose the operating system based on a large number of factors. The choice of OS will then dictate what options you have for selecting DHCP server software. Most common operating systems have a number of options available for software. While all will implement the core DHCP protocol, they will differ in terms of the usual software attributes: cost, performance, ease of use and so. They may also differ in terms of their features, such as the following:

• How they allow address ranges (scopes) to be defined.
  
  
• How clients can be grouped and managed.
  
  
• The level of control an administrator has over parameters returned to a client.
  
  
• The level of control an administrator has over general operation of the protocol, such as specification of the T1 and T2 timers and other variables, and how leases are allocated and renewals handled.
  
  
• Security features.
  
  
• Ability to interact with DNS to support dynamic device naming.
  
  
• Optional features such as BOOTP support, conflict detection, and automatic private IP addressing.

In setting up DHCP for a network, there are a number of important factors to consider and decisions to be made. One of the most critical is the number of servers you want to have. In theory, each network requires only one DHCP server; in practice, this is often not a great idea. Servers sometimes experience hardware or software failures, or have to be taken down for maintenance. If there is only one server and clients can't reach it, no DHCP clients will be able to get addresses. For this reason, two or more servers are often used.

If you do use more than one server, you have to carefully plan how you will configure each one. One of the first decisions you will need to make is which servers will be responsible for which addresses and clients. You have to determine whether you want the servers to have distinct or overlapping address pools, as discussed in the topic on DHCP address ranges. Distinct pools ensure that addresses remain unique but result in unallocatable addresses if a server fails; overlapping addresses are more flexible, but risk address conflicts unless a feature like conflict detection is used.

DHCP Client/Server Implementation, Features and Issues 1 2 3 DHCP Client General Implementation and Management Issues