Upload speed slow in Windows through ipv6

[Chengbo Zhao]

Hello:

I just changed my way back home from OpenVPN to WireGuard. Nice work,
faster and easier to configure!

But when I tried to connect through ipv6, I had some troubles: the
download speed seems normal, but upload speed (Both to LAN and WAN)
was limited to ~10Mbps (about 10~20% of full speed).

I thought it was a network issue at first, so I used a process of
elimination to find out what went wrong. On the mobile phone, using
the same configuration, both upload and download can reach the upload
rate of my broadband ~60Mbps. This indicates that the computer may not
be working properly. So, I went on to test on my laptop and found that
when using ipv4 for connection, the upload and download can also run
at full speed. I guess that there may be a performance problem with
the forwarding of ipv6 packets in WireGuard NT. By the way, I just
configure ipv4 for all clients in WireGuard's internal network.

  Test Device     ipv4-download   ipv4-upload   ipv6-download   ipv6-upload
 --------------- --------------- ------------- --------------- -------------
  PC-Win11        ~60Mbps         ~60Mbps       ~60Mbps         ~10Mbps
  Phone-Android   ~60Mbps         ~60Mbps       ~60Mbps         ~60Mbps

Can you guys do further tests to resolve this issue?

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Thanks,
Chengbo Zhao