Specifications

Chapter 3 Connecting on a LAN
Using DHCP
Niagara Release 2.3
Niagara Networking & Connectivity Guide Revised: May 22, 2002
3–31
Lease Renewal Failure
Per the DHCP specification, a Windows host will periodically renew its lease, even
when using a reserved address. The DHCP server defines the length of the renewal
period. If the renewal request ever fails (for example, if the DHCP server is offline,
or the Ethernet cable is disconnected when the renewal request occurs) and the lease
expires, then one of the following things occurs:
• Windows NT 4.0 host—disables its network interface. This follows the
DHCP specification, and it was written that way to prevent a host from using
an IP address for which it no longer has a valid lease.
When a host has failed to renew its lease, it cannot be accessed using the
Ethernet connection. To fix this problem, correct the problem that caused the
renewal to fail, and reboot the host.
• Windows 2000 host—the computer assigns itself an IP address in the private
Class B range of 169.254.0.0 with a subnet mask of 255.255.0.0. No gateway
or DNS server is assigned. This is a new feature of Windows 2000 called
automatic IP addressing.
To fix this problem, correct the problem that caused the renewal to fail. When
the DHCP server becomes able to service requests, the host will update its
address information.
DHCP Reservation not Working
If the DHCP administrator has set up the reserved address, but the JACE fails to pick
it up on the initial boot after you enabled DHCP, then you may have given the DHCP
administrator the wrong MAC address. Verify the MAC address of the host using
“Determining the MAC address of a Niagara host.,” page 3-23 or with the
ipconfig
command (see the next section “Using the ipconfig Command”).
However, if the JACE receives the reserved IP address, but upon renewal of its
DHCP lease gets assigned another IP address, then the fault may lie with the DHCP
reservation. In the DHCP server is Windows-based, the reservation must be made on
both the primary DHCP server and any backup DHCP servers that handle the same
DHCP scope. A DHCP scope is a range of IP addresses that the server can assign. If
the scope can be assigned from multiple servers, then each server must also have
reservations listed for the scope. To determine which DHCP server handled the last
DHCP request for the JACE, see the
ipconfig command.
Using the ipconfig Command
The primary troubleshooting utility used with DHCP on a Windows-based host is
ipconfig (see the “ipconfig” section on page 2-27). In Example 3-4, information
concerning the DHCP setup of a Windows 2000 host is highlighted (similar
information is available for a Windows NT 4.0 host). A discussion of each
highlighted item follows the example.