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We have PC's that switch IP's when they go between wired and wireless access to our network. Unfortunately when a PC goes from wireless to wired, all the other computers on the network are not made aware about the new IP and they try to hit the computer using the old IP.

What needs to be done to configure the network to seamlessly retain the network access-ability of a PC when it switches between wired/wireless?


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So you have a server on your wireless network? Probably not a great idea. – EEAA Apr 26 '11 at 16:36
No, these are laptops. This is probably more appropriate for SuperUser but I figured more network guys would be here. – Matias Nino Apr 26 '11 at 16:44
@Matias - no, if other computers are trying to "hit the computer", it's a server regardless of whether or not it's using server-class hardware. – EEAA Apr 26 '11 at 16:49
So you are essentially saying that having a computer share files (e.g. be a "server") over a wireless network is not a good idea? That's pretty absurd. – Matias Nino Apr 26 '11 at 18:10
@Matias - yes, that's what I'm saying. Additionally, having a server whose IP is not stable is equally as concerning. Put your file shares on a centralized "server" - one that is connected to your network by good ol' Cat6 (or Cat5e, I suppose) cable, and give it a static IP address. – EEAA Apr 26 '11 at 18:58

Short answer: Name Resolution

Long answer: Depends what you're using, DNS or/and WINS you might be able to run appropriate scripts to make the machine that you switch between networks to update it's own info in the DNS or/and WINS. However, the problem here is to have all the rest of the machines to be aware of the change, which basically means, make them purge their own resolution cache and go to the DNS/WINS look up to ask for the new name. This as well can be accomplished by reducing or even removing the TTL for the cache on each and every machine to a minimum possible, or disable it altogether.

I assume you understand how it will impact your network as well as the servers that are responsible for name resolution. Obviously, the impact will be pretty huge.

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Thanks. Right now it takes about 10 minutes for all the computers to become aware of the change. This may be acceptable for most computers. We can manually purge those that we need aware of the change right away. Thanks! – Matias Nino Apr 26 '11 at 16:49

However un-ideal this situation may be, your best option is probably to setup a CNAME entry in your DNS pointing to the A record of the laptop (i.e. Server). This way clients cache the CNAME record rather than the A record and DNS server will be responsible for handling the IP resolution. Have the users connect using the CNAME entry.

CNAME of resource.domain
A Record of laptop.domain

When the laptop changes it's IP between connections it will update the A/ PTR record which will then be reflected in the CNAME record.


I thought about this again and my answer still does not solve the issue. Even with the CNAME record clients will still cache the response they receive back from the DNS server. You would need to stop the clients from caching responses or lower the cache time. You could do so with editing the DWORD value MaxCacheTtl &MaxNegativeCacheTtl found at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters. change these values to how many seconds you want to cache entries. Reference: Disable Client-side DNS caching

Be aware of the impact this will have on your network/ clients.

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