If an autoconfigured IPv6 address for some reason falls into deprecated state (eg if no router advertisement is received within the preferred lifetime) it appears that even if at this stage a router advertisement is received containing this prefix, the address stays as deprecated even though the timers are reset. If one has a look in netsh (netsh -> int -> ipv6 -> show addr) one will find that the entry for the advertised public prefix has these seemingly conflicting properties: DAD state: Deprecated Valid life: the appropriate time according to the received RA Pref. life: the appropriate time according to the received RA Example from testing (I set the preferred life for the prefix really low (30s) to reproduce the problem quickly): Normal working state (normal): Addr Type DAD State Valid Life Pref. Life Address --------- ----------- ---------- ---------- ------------------------ Public Preferred 23h59m58s 28s 2001:470:xxxxxxxxxxxxxxx No advertisement received before end of life time (normal): Addr Type DAD State Valid Life Pref. Life Address --------- ----------- ---------- ---------- ------------------------ Public Deprecated 23h58m24s 0s 2001:470:xxxxxxxxxxxxxxx Advertisement received that matches deprecated address (assumed bug): Addr Type DAD State Valid Life Pref. Life Address --------- ----------- ---------- ---------- ------------------------ Public Deprecated 23h59m57s 27s 2001:470:xxxxxxxxxxxxxxx The non-zero preferred lifetime combined with deprecated state appears inconsistent! One would think the state should go back to preferred at this point (which would lead to Windows being able to use the address again). At that stage the only way to bring the ipv6 stack in Windows back into a working state appears to be to toggle IPv6 on the interface, disable/enable the interface entirely (or unplugging and plugging back the ethernet cable, I suppose) to reset the state. However I don't believe it should be possible for Windows to get stuck in that state to begin with...?

Hi, I think the router advertisement can be from hardware router. Regards, Sabrina TechNet Subscriber Support in forum. If you have any feedback on our support, please contact tngfb@microsoft.comThis posting is provided "AS IS" with no warranties or guarantees, and confers no rights. |Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Yes, absolutely, the router advertisement comes from a router... The issue is: How come Windows doesn't restore the state of the autoconfigured IPv6 address from Deprecated to Preferred in the scenario described above?

I have noted that IPv6 issues posted here in general seem to be referred to the Windows server IPv6 forum that I initially overlooked, so I posted my question there.