Update docs

- Add info about IPv6 traffic
- Closes #480. Thanks @sunfeilong!

docs/clients-zh.md

@@ -241,6 +241,8 @@ Windows Phone 8.1 及以上版本用户可以尝试按照 <a href="http://forums
 
 Windows 8.x 和 10 默认使用 "smart multi-homed name resolution" （智能多宿主名称解析）。如果你的因特网适配器的 DNS 服务器在本地网段上，在使用 Windows 自带的 IPsec VPN 客户端时可能会导致 "DNS 泄漏"。要解决这个问题，你可以 <a href="https://www.neowin.net/news/guide-prevent-dns-leakage-while-using-a-vpn-on-windows-10-and-windows-8/" target="_blank">禁用智能多宿主名称解析</a>，或者配置你的因特网适配器以使用在你的本地网段之外的 DNS 服务器（比如 8.8.8.8 和 8.8.4.4）。在完成后<a href="https://support.opendns.com/hc/en-us/articles/227988627-How-to-clear-the-DNS-Cache-" target="_blank">清除 DNS 缓存</a>并且重启计算机。
 
+另外，如果你的计算机启用了 IPv6，所有的 IPv6 流量（包括 DNS 请求）都将绕过 VPN。要在 Windows 上禁用 IPv6，请看<a href="https://support.microsoft.com/zh-cn/help/929852/guidance-for-configuring-ipv6-in-windows-for-advanced-users" target="_blank">这里</a>。
+
 ### macOS VPN 流量
 
 OS X (macOS) 用户： 如果你成功地使用 IPsec/L2TP 模式连接，但是你的公有 IP 没有显示为 `你的 VPN 服务器 IP`，请阅读上面的 [OS X](#os-x) 部分并完成这一步：单击 **高级** 按钮，并选中 **通过VPN连接发送所有通信** 复选框。然后重新连接 VPN。

docs/clients.md

@@ -241,6 +241,8 @@ After upgrading Windows 10 version (e.g. from 1709 to 1803), you may need to re-
 
 Windows 8.x and 10 use "smart multi-homed name resolution" by default, which may cause "DNS leaks" when using the native IPsec VPN client if your DNS servers on the Internet adapter are from the local network segment. To fix, you may either <a href="https://www.neowin.net/news/guide-prevent-dns-leakage-while-using-a-vpn-on-windows-10-and-windows-8/" target="_blank">disable smart multi-homed name resolution</a>, or configure your Internet adapter to use DNS servers outside your local network (e.g. 8.8.8.8 and 8.8.4.4). When finished, <a href="https://support.opendns.com/hc/en-us/articles/227988627-How-to-clear-the-DNS-Cache-" target="_blank">clear the DNS cache</a> and reboot your PC.
 
+In addition, if your computer has IPv6 enabled, all IPv6 traffic (including DNS queries) will bypass the VPN. Learn how to <a href="https://support.microsoft.com/en-us/help/929852/guidance-for-configuring-ipv6-in-windows-for-advanced-users" target="_blank">disable IPv6</a> in Windows.
+
 ### macOS VPN traffic
 
 OS X (macOS) users: If you can successfully connect using IPsec/L2TP mode, but your public IP does not show `Your VPN Server IP`, read the [OS X](#os-x) section above and complete this step: Click the **Advanced** button and make sure the **Send all traffic over VPN connection** checkbox is checked. Then re-connect the VPN.