DHCP Duplicate IP Detection is marking the IP address as Bad_Address when
the response is "host unreachable". Duplicate IP detection code should
read the ICMP packet and do nothing if the host is unreachable, instead of
marking the address as if a valid response was received. Bad_Address
flagging is part of the Duplicate IP Detection feature added to Windows NT
4.0 in Service Pack 2.
Bad_Address indications are being caused by a Windows for Workgroups 3.11
bug that occurs when all of the following conditions are present:
- Windows for Workgroups 3.11b clients are present on the network.
- At least two DHCP servers are present on the network, and at least
one of them has Duplicate IP Address Detection enabled.
- The DHCP servers are separated from the Windows for Workgroups
clients by a router.
- The router has ARP cache enabled.
- The router has the BOOTP relay agent enabled.
The DHCP server receives a "Destination Host Unreachable" packet as a
result of the client bug and the behavior of DHCP's Duplicate Address
Detection. By current design, DHCP marks the IP address as BAD_ADDRESS if
there is ANY response to ICMP echo request.
To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the
Microsoft Knowledge Base:
How to Obtain the Latest Windows NT 4.0 Service Pack
You can work around this problem by doing one of the following:
- Upgrade all WFWG clients to Windows 95 or Windows NT clients.
- Disable the ARP cache on the CISCO router. (ARP cache is enabled by
default on most routers.)
Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.
The problem occurs in the following scenario:
- The Windows for Workgroups client broadcasts an IP address request (a
DhcpDiscover packet) to the two DHCP servers.
- The first DHCP server responds to the request and assigns an IP address
to the client through the normal sequence of DHCP handshaking between
it and the client. The client binds to the given IP address.
- As part of Duplicate IP Address Detection , the second DHCP server
sends an ICMP echo packet to the IP address it is attempting to assign
(that is, the next available address in its pool). This is to confirm
that the address is not already in use.
- Because the router has ARP cache enabled, it associates the media
access control address of the Windows for Workgroups client to the IP
address already assigned to the client from the first DHCP server. It
then sends the ICMP echo packet to the media access control address of
the Windows for Workgroups client.
- The client receives the packet, but the packet contains a different IP
address (the one from the second DHCP server) than the one it has bound
to its stack. Because of this address discrepancy, it responds back to
the server with "Destination Host Unreachable".
- When the second DHCP server with Duplicate Address Detection receives
an ICMP error response "Host Unreachable". The Error code is set to
Article ID: 187802 - Last Review: November 1, 2006 - Revision: 2.3
- Microsoft Windows NT Server 4.0, Terminal Server Edition
- Microsoft Windows NT Server 4.0 Standard Edition
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