Non-rfc Compliant DHCP Server Does Not Send DHCPNAK When Client is Moved to Another Subnet

SUMMARY

When a Windows NT DHCP client is moved to another subnet (without issuing the ipconfig/release command before moving), the client will request its previous IP address. Usually this IP address is not valid for usage on the new subnet.

When a DHCP server detects that the client requests an IP address that does not fit for the current subnet, the DHCP server must send a DHCPNAK to the client (according to RFC1541).

Some non-rfc compliant DHCP servers do not send this DHCPNAK. Because of this, the client does not attempt to lease a new IP address on the new subnet and tries to use its old IP address (see the frame information later in this article).

This problem has been experienced only when using a third-party DHCP server. The Microsoft Windows NT DHCP server does not experience this behavior.