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Multi site DHCP/IP issue

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by cscott 1 view

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Here's the problem. I have a user who uses DHCP at multiple sites on a Dell Win98se laptop(one at home on the cablemodem, one at work Nt4 server) to obtain an IP address. At home the user has no trouble getting an ip from the cable dhcp. At work he sometimes gets the can't find Domain server and his machine attempts to use his 24.x.x.x ip from his last home connection. The server notices this and issues a nack. I can release this IP and when I renew, the machine successfully picks up an IP fromthe server and all is well. Any thoughts? No other machine on the network is having this problem. Originally I installed a program called Netswitcher that controlled his multiple site IP switching since at work he has mapped drives. For months when this user logged in he would find the domain server just fine but would attempt to use his cablemodem ip as reported by Event Viewer. IPX is also installed at work. Apparently a valid ip would still be issued to him after this invalid ip request and he was none the wiser. Now we have this new issue. A strange issue indeed. Please let me know what other information I can provide to assist in troubleshooting. Thanks.

13 replies

by curacao_dejavu

See the MS KB Q229882

When an Internet Connection Sharing (ICS) host computers starts and logs on to the network, client computers may experience a delay in receiving an IP address from the ICS host. Clients may receive the following error message:

DHCP Server Unavailable: Renewing Adapter.

RESOLUTION
To work around this issue, wait 60 seconds after the client receives the "DHCP Server Unavailable" error message, click Start, click Run, type winipcfg, click OK, and then click Renew All.

If the issue persists, refer to the Internet Connection Sharing Troubleshooter on the ICS host computer by clicking Start, clicking Help, clicking the "Troubleshooting" topic, then the "Windows Troubleshooters" topic.

MORE INFORMATION
This issue can occur because of the following behavior: To avoid conflicts with other DHCP servers, the ICS host sends out a DHCP Discover packet at startup and every 60 seconds afterward. ICS DHCP services stop if another DHCP server is located. This delays the ICS host's ability to receive and correctly respond to the clients' Bootp requests.

problem is , he is using that computer as a ics for his other computers at home.

Leopold

by cscott

No internet connection sharing at all here. Just two DHCP servers. With the 1st home IP on the machine the computer cannot receive a new ip from the work DHCP server. After it is manually released and renewed it picks up the server and gets an ip.

by ryder007

Hi this I guess is more of a question than a answer, if the user is still logging on as a network client at home perhaps that causes the problem when he brings it back to work because it still has the modem dhcp. Maybe when he turns the comp on at home he should not log on with any password. I'm sorry that it's not much help, but it is a very interesting problem.

by alciur22

I would set up 2 hardware and user profiles for the laptop. Set all configurations to each profile and when the user logs on at home use the home profile and when at work use the work profile.

AL

by tlippert

Stick another cheap nic in the laptop and use one for the work network and the other for home. If this was win2k you could do this with one nic and two slots. Win2k remembers the ip address based on the slot used.

by vh_s

It is a very interesting problem indeed.

I just couldn't make up why would you use Netswitcher for IP switching. What mapped drives have to do with this ?

Sorry, just need more details to understand your problem correctly..

by scviking

This is a normal occurrence when you have a laptop using two different DCHP servers. The laptop is still using an IP leased from his cable ISP when the user hooks it up to his work network; hence, the DNS errors. (I work for a DSL provider and see this problem about 4x a day)

The IP lease hasn't expired or been released, so it assumes that the connection to the cable modem is still valid and tries to access your work network using the 24.x.x.x IP.

The reason you can successfully release and renew the IP and get an IP from your DHCP server at work is also why no other machine on the network is having a problem as well. All of your computers, including the laptop, are configured correctly- it's simply a quirk in the way DHCP servers work, believe it or not.

Adding a second NIC or even a second hardware profile will only complicate the problem needlessly. Logging off and logging on again may work, but isn't even necessary.

The flaw is simply in the way DHCP leases out IP addresses, so even lowering the lease times on your DHCP server at work won't solve the problem. You're never going to get the leases on both networks synchronized, and lowering the lease times on your work network will increase network traffic and could cause other problems.

There's actually nothing wrong with any of the DHCP servers, or the laptop, or any of the other machines on the work network.

However, there are a few 'fixes':

1) Teach your user how to manually release and renew his IP address at work.

2) Make certain that your user reboots his laptop after he hooks up his laptop to the network at work. Rebooting automatically releases and renews the IP (and flushes the memory and other good things). If the user is just plugging his laptop in while it's on standby, the problem won't go away.

The problem is with user expectations here, not the network.....

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