Windows IPv6 connection starting to "rot" over time [Solved!]
Tuesday, August 27. 2013
I've been using IPv6 on my own LAN for years. Most of the things I use on daily basis have IPv6 and it seems to work. For example a Sony television or iPhone 4S does not use IPv6, but iPad does.
On my router there is a Router Advertisement Damon to do stateless auto-configuration. On Windows 7 and 8 they have really weird things running out-of-the-box, but I'm in a habit of running (as admin):
netsh interface ipv6 set privacy state=disabled store=active
netsh interface ipv6 set privacy state=disabled store=persistent
netsh interface ipv6 set global randomizeidentifiers=disabled store=active
netsh interface ipv6 set global randomizeidentifiers=disabled store=persistent
netsh interface teredo set state disabled
That way I'm using fixed IPv6-addresses and disable the unnecessary Teredo-tunnel.
I don't exactly know why or how, but on one of my computers (running Windows 7), the IPv6-sockects started to not work properly. The symptoms include lot of reconnections and for example in SSH-client, the connection would simply drop. I did everything I knew, but nothing helped. A failing SSH-connection would look like this on the wire:
After 31 seconds of connection, there is a sporadic retransmission. That is not dangrous and it happens sometimes. My Windows 7 would respond with a duplicate ACK into it, waits 3 seconds and goes ballistic. It simply starts re-transmitting the already transmitted data with 1, 3 and 5 second intervals before determining that the connection has died. WTF?! The connection is not bad! It works on all other computers. The issue can be easily repeated and it works the same way every time. Windows thinks it needs to start a burst of re-transmissions and disconnects when they seem to fail.
During one of the Google-session for the fix, I found netsh interface ipv6 reset command. I tried it:
PS C:\Windows\system32> .\netsh.exe interface ipv6 reset
Reseting Global, OK!
Reseting Interface, OK!
Reseting Subinterface, OK!
Restart the computer to complete this action.
Did the Windows restart, ran the above commands to disable privacy, randomization and teredo-tunnel. Everything started to work! Whooo-hoo! Now my SSH-connections don't drop anymore. How cool is that!
The fix is very microsoft-ish. Some counter ticked into illegal value and in their mind the correct fix is to reset everything to the post-installation state. On *nix-world network-stack -code would be of much better quality and the entire issue would never happen!
