Microsoft KB Archive/272076

= Windows 2000 NAT DHCP Allocator Service Logs Event 30001 =

Article ID: 272076

Article Last Modified on 2/28/2007

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server

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This article was previously published under Q272076



SYMPTOMS
A Windows 2000-based server running the Network Address Translation (NAT) service with the DHCP allocator function may log the following system event

Source: ipnathlp

Event ID: 30001

Category: None

Type: Warning

Description: The DHCP allocator was unable to check whether the IP address  is in use on the network for local IP address. This error may indicate lack of support for address-resolution on the network, or an error condition on the local machine. The data is the error code.

where  is the IP address that NAT is attempting to lease out to a client, and   is the IP address of the interface running the DHCP allocator service in NAT.



CAUSE
There is a host on the network which has a duplicate of an IP address in NAT's DHCP pool of addresses.



RESOLUTION
To resolve this issue, use either of the following methods:
 * Change the IP address on the offending host (that which already has the IP address).
 * Exclude the specific IP address from the DHCP allocator range in NAT.

You can identify the host with the undesired duplicate IP address in one of the following ways:  On the NAT server's ARP cache, there may be a mapping of the IP address in conflict to the MAC address of the offending computer. The network administrator would then need to determine which specific computers had the given MAC address. To display the ARP cache on the NAT server, perform the arp -a command on the NAT server at a command prompt. In some circumstances the DHCP client may display a message indicating the conflict and specifying the MAC address of the offending computer. Temporarily remove the DHCP client from the network, and from a Microsoft machine on the network, perform the following command at a command prompt

nbtstat -a 

where  is the address in conflict. If the offending host on the network is running a Microsoft operating system, the above command should return a list of the NetBIOS names the remote host is listening on. This may assist you in further determining which specific computer has the address in conflict.

To suppress the error message from being written to the event log, change the logging level of the NAT service to log errors only. This does not resolve the root cause of the problem, but it does prevent the warning from being logged in the system log.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.



MORE INFORMATION
Before the DHCP allocator service in NAT gives a client a lease for a particular IP address, it sends an ARP request for the IP (a gratuitous ARP) to see if the address is already in use. If a computer (or network device) responds to this ARP request, the DHCP allocator service logs this warning, and tries to issue the next available IP address in the DHCP scope.

Keywords: kbenv kberrmsg kbnat kbprb KB272076

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