This describes the behavior of the DHCP server in the Netopia Router.

Problem:

All Netopia routers come with an integrated Dynamic Host Control Protocol (DHCP) server. These servers provide a means of distributing IP addresses to either a Mac or PC workstation as needed. This Technical Note describes how the workstations interact with the DHCP server within the Netopia router.

Parameters:

Below is a list of hardware and firmware loads that this Technical Note is based upon:

Network Configuration:

Below is a diagram of the network referenced in this Technical Note.

Background:

When setting up the DHCP server in the Netopia router, it is necessary to understand how workstations lease, renew, and release their IP addresses. This information will be helpful in determining dynamic address allocation for a network.

The term "lease" describes the action of a workstation requesting and using an IP address. The address is dynamic and can be returned to the address pool at a later time.

The term "renew" refers to what the workstations do to keep their leased IP address. At certain intervals, the workstation talks to the DHCP server and renews the lease on that IP address. This renewal allows the workstation to keep and use the assigned IP address until the next renewal period.

The term "release" refers to a situation where the workstation is no longer using its assigned IP address or has been shut down. IP addresses can be manually released as well. The IP address goes back into the DHCP address pool to be reassigned to another workstation as needed.

Configuration:

This section describes the specific IP address lease, renew and release mechanisms for both the Mac and PC, with DHCP address serving.

DHCP Address Serving:

Windows 95/98 & NT Workstation

• The Windows workstation requests and renews its lease every half hour.
• The Windows workstation does NOT relinquish its DHCP address lease when the machine is shut down.
• The lease can be manually expired using the WINIPCFG program from the Win95/98 machine, or using IPCONFIG on the NT, which is a command line program executable from the DOS prompt or from the START:RUN menu.

Macintosh Workstation (Open Transport Version 1.1 or later)

• The Mac workstation requests and renews its lease every half hour.
• The Mac workstation will relinquish its address upon shutdown in all but one case. If the TCP/IP control panel is set to initialize at startup, and no IP services are used or the TCP/IP control panel is not opened, the DHCP address will NOT be relinquished upon shutdown. However, if the TCP/IP control panel is opened, or if an IP application is used, the Mac WILL relinquish the lease upon shutdown.
• If the TCP/IP control panel is set to acquire an address only when needed (therefore a TCP/IP application must have been launched to obtain a lease) the Mac WILL relinquish its lease upon shutdown every time.

Netopia DHCP Server Characteristics

• The Netopia ignores any lease-time associated with a DHCP request and automatically issues the DHCP address lease for one hour.
• The Netopia does release the DHCP address back to the availible DHCP address pool precisely one hour after the last heard lease request as some other DHCP implementations may hold on to the lease for an additional time after the lease expired, to act as a buffer for variances in clocks between the client and server.

Summary:

This Technical Note describes how either a Mac or PC workstation interacts with the DHCP server within the Netopia router. For more specific information on the setup and configuration of the DHCP server within the Netopia router, please see the Netopia Router Reference Guide.