This article was previously published under Q167014
When a DHCP client is moved from one subnet to another, it may fail toobtain a valid IP address on the new subnet.
To work around this problem, do one of the following methods:
Do not use IP addressing schemes that overlap.
Run the following commands after you move the client to a new segment:
Ipconfig /Release Ipconfig /Renew
When a DHCP client that has previously had a DHCP-assigned address isstarted again, the client goes into an INIT-REBOOT state. The client willattempt to verify that it can still use the same address by sending aDHCPRequest packet, populating the DHCP Option Field "DHCP RequestedAddress" with the previously assigned IP address.
If the DHCP server remains silent, the client assumes the previous addressis still valid and keeps it. If a DHCP server sends a NACK packet inresponse to the DHCPRequest, the client goes into the Discover cycle;it also requests the previously assigned address in the DHCPDiscoverpacket.
When a DHCP server receives a DHCPRequest with a previously assignedaddress specified, it first checks to see if it came from the local segmentby checking the GIADDR field. If it originated from the local segment, theDHCP server compares the requested address to the IP address and subnetmask belonging to the local interface that received the request.
If the address appears to be on the same subnet, the DHCP server willremain silent even if the address is not in the range of its pool ofaddresses. The DHCP server assumes that the address was assigned byanother DHCP server on the same segment if it is not from its own pool. Ifthe address fails the subnet mask/IP address check, the DHCP serverchecks to see if it came from a Superscope, if one is defined. If not,the server responds to the DHCPRequest with a NACK packet.
If the client sending the DHCPRequest is requesting an address that appearsto be on the same subnet but was actually assigned with a different subnetmask, the DHCP server will remain silent and the client will fail to obtaina valid IP address for the new subnet.
For example, assume the DHCP client obtains address 172.17.3.x with asubnet mask of 255.255.255.0, and the client is moved to a new segmentwhere the address of the DHCP server is 172.17.1.x with a subnet mask of255.255.0.0. When the subnet mask/IP address comparison is done on the DHCPserver, the DHCP server will remain silent, assuming another DHCP server onthe segment assigned the address. If the subnet masks were reversed, theclient would obtain a valid address.
رقم الموضوع: 167014 - آخر مراجعة: 02/26/2007 23:34:53 - المراجعة: 3.3
Microsoft Windows Server 2003, Enterprise Edition (32-bit x86), Microsoft Windows Server 2003, Standard Edition (32-bit x86), Microsoft Windows 2000 Server, Microsoft Windows 2000 Advanced Server, Microsoft Windows 2000 Professional Edition, Microsoft Windows 2000 Datacenter Server, Microsoft Windows NT Workstation 3.5, Microsoft Windows NT Workstation 3.51, Microsoft Windows NT Workstation 4.0 Developer Edition, Microsoft Windows NT Server 3.5, Microsoft Windows NT Server 3.51, Microsoft Windows NT Server 4.0 Standard Edition, Microsoft Windows for Workgroups 3.2, Microsoft TCP/IP-32 for Windows for Workgroups 1.0, Microsoft Windows 95