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 Address Assignment and Dynamic Address Allocation and Management

DHCP Address Assignment and Allocation Mechanisms 1 2 3 4 DHCP Lease "Life Cycle" Overview (Allocation, Reallocation, Renewal, Rebinding and Release) and Lease Timers

Common Lease Durations

The administrator need not pick from “short” and “long” lease durations. He or she can “compromise” by choosing a number that best suits the network. Some examples of lease times and the reasoning behind them:

• One Hour Or Less: Ensures maximum IP address allocation efficiency in a very dynamic environment where there are many devices connecting and disconnecting from the network, and the number of IP addresses is limited.
  
  
• One Day: Suitable for situations where “guest” machines typically stay for a day, to increase IP efficiency when many employees work part-time, or otherwise to ensure that every day each client must ask again for permission to use an address.
  
  
• Three Days: This is the default used by Microsoft. This alone makes it a popular choice.
  
  
• One Week: A reasonable “compromise” between the shorter and longer times.
  
  
• One Month: Another “compromise”, closer to the longer end of the lease time range.
  
  
• Three Months: Provides reasonable IP address stability so that addresses don't change very often in reasonably static environments. Also a good idea if there are many IP addresses available and machines are often turned off for many days or weeks at a time. May be used in a university setting to ensure that IP addresses of returning students are maintained over the summer recess.
  
  
• One Year: An approximation of an “infinite” lease; see below.

In fact, not only is the administrator not restricted to a limited number of possible lease durations, it is not necessary for the administrator to choose a constant lease length policy for all clients. Depending on the capabilities of the DHCP server, an administrator may select different lease lengths for certain clients than others. For example, the administrator may decide to use long leases for desktop computers that are permanently assigned to a particular subnet and not moved, and a pool of short-leased addresses for notebooks and “visitors”. In some DHCP implementations this can be done by assigning clients to particular “classes”. Of course, this requires more work (and may even require multiple servers.)

DHCP Address Assignment and Allocation Mechanisms 1 2 3 4 DHCP Lease "Life Cycle" Overview (Allocation, Reallocation, Renewal, Rebinding and Release) and Lease Timers