DHCP having issues

[richh70]

When a user shut of there PC or unplugged from the network then retry to connect to the network they are not getting an IP address. Do anybody have any suggestions to what could be the problem or what could have cause this issue.

[Bill Castner]

There can be several reasons for this behavior.

First, make sure the problem client has no issues with its Winsock2 service stack. For XP with Service Pack 2:

Start, Run, CMD
netsh winsock reset

Wait for a response that a restart is needed. Restart the computer.

This should only have to be done once to repair the TCP/IP Winsock service stack.

Second, the common reason for this is that the user is moving between physical networks that employ the same IP address scope. For example, a laptop user brings the computer home. At home, a router is used to assign IP and other addressing details, just as at work. Both at home and at work the same address range is used for DHCP -- lets say as an example, 192.168.1.x.

When the user connects back again at his workplace LAN, the DHCP server will find an existing IP address within its DHCP scope. If the subnet mask in use by the client is the same or larger in scope the DHCP server will assume the IP address was assigned by a different DHCP server in a WAN setting and remain silent.

If the DHCP server remains silent, the client assumes the previous address is still valid and keeps it. Since in this case no lease was obtained, the address is in fact invalid. http://support.microsoft.com/?kbid=167014

Methods to repair DHCP services when this happens:

• Do not use IP addressing schemes that overlap.
This is easier said than done if the client is travelling to other workplace sites. If the issue is a frequent one between a Home LAN and the workplace LAN, show the user how to change the Home LAN DHCP scope of addresses. For example, in this case advise the user to use a different IANA private IP range completely on the Home LAN router.

• When you cannot use different IP addressing schemes, write a small .cmd script and create a user desktop shortcut to point to it. The simple .CMD script would contain two lines:

Ipconfig /Release
Ipconfig /Renew

Now the DHCP request should succeed. It it fails at this point, some other basic TCP/IP connectivity issue is at fault.

[richh70]

The user are unable to pull a IP address once they are disconnect from the network and try to reconnect. This is happening to users on different subnets throught the work place. The problem has been fix by restarting the DHCP services. But i am unassure as to why this happen. Do anybody have any suggestions?

[chicagotech]

Since this is different subnet, how do you setup your network? Do you have a router between two different subnet? We need more details to help.