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I'm in the process of exploring IPv6 deployment in my network. I've changed the advertised subnet and now my windows PCs have IPs from the new and the old network.

I was able to reset the adapter by unplugging the cable, but this is of course no long-term solution.

How can I force windows to forget the "wrong" IPs?

I'm using Windows 7 and Windows Server 2008 as clients, and radvd on squeeze as router.

I've tested ipconfig's /release and /release6, but both do not affect the autoconfigured addresses.

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up vote 2 down vote accepted

IPv6 has a more explicit support for migrating IP addresses. Changing your advertised subnet is supposed to be transparent to your users. When a new address is available new connections will use that new IP address. Old connections will still use the old address. Eventually the address should be removed but not before all old connections have stopped using the address.

You might need to make sure that no connections are listening on the old IP address (netstat is your friend here).

In any case as long as the old address is not causing any harm it should not be a problem. What is the metric for this address? Is it being used for new connections?

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It turned out that the problems I was seeing stemmed from the fact that the server in question found itself in a new network environment and thus went to "Public" security settings. Regarding the question I wrote, your answer seems sensible: support both nets until the old addresses time out. – David Schmitt May 27 '11 at 9:36

Once you change the prefix your router is advertising, addresses in the old subnet will be deprecated and eventually removed without any intervention on your part. The address will be deprecated for the difference between the preferred and valid lifetimes advertised by your router. (On my network this works out to 90 minutes, but it depends on how you configured radvd.)

To see deprecated addresses on your Windows network interfaces you can use netsh interface ipv6 show address, or PowerShell Get-NetIPAddress -AddressFamily IPv6.

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You'll need to remove all cached/autoconfigured IPv6 settings then let them repropagate. The command on Windows is

netsh int ipv6 reset

You'll need to restart for the changes to take effect.

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Powershell with Administrator Rights

Show ip addres: netsh interface ipv6 show address
Delete ip/use Interface name: netsh interface ipv6 delete address Ethernet0 200x:x:x:x:x:x:x:x
netsh interface ipv6 delete address (Interface index or name) (ipv6address)

Show routes: netsh interface ipv6 show route
Delete route: netsh interface ipv6 route delete 200x:x:x:x::/64 Ethernet0 store=persistent
netsh interface ipv6 route delete (ipv6prefix::/64) (Interface Index or Name)

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At the command prompt,

ipconfig /release

The Syntax and Options for Using the Ipconfig Diagnostic Utility for Network Connections

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On Windows7/2008, /release only drops DHCPv4 addresses. There is a /release6 switch, but this doesn't seem to affect the autoconfigured addresses. – David Schmitt May 25 '11 at 18:27

The only way that worked for me was to physically unplug the network cable and then plug it back in.

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