ECN on Windows

[Demi-Marie]

This might be possible, although the APIs are undocumented.

[Ralith]

It would be useful to cite evidence.

[Demi-Marie]

Receiving ECN is possible via the IP_RECVTOS option at IPPROTO_IP and the IPV6_RECVTCLASS option at IPPROTO_IPV6. Setting is definitely possible if one has administrative privileges. I am not sure about otherwise.

[Demi-Marie]

Setting it might be possible via the undocumented IPV6_ECN and IP_ECN socket options.

[Demi-Marie]

As per microsoft/msquic#559 (comment) I don’t believe this is supported on current versions of Windows. Closing.

[Demi-Marie]

Reopening in light of microsoft/msquic#559 (comment) which actually implements ECN in MsQuic. Since msquic.dll is not an OS-provided DLL, I am confident that this will continue to work in future releases of Windows.

[panxy2013]

in microsoft document, we can write UDP client / server, and use wirshark can find, IP ECN 2bits can be modify by windows socket API WSASendMsg

but how to use in Rust, does quinn-udp can support such action?

1. send UDP with ECN bit = 0x01 or 0x02
2. Recieve UDP and can get ECN bit from receive UDP packet

https://learn.microsoft.com/en-us/windows/win32/winsock/winsock-ecn

Thanks

[djc]

We don't support this yet in quinn-udp, would you be able to send a PR to use windows-sys APIs to implement this?

[panxy2013]

Well, since I'm newer to Rust, I don't have the ability to write good Rust code at the moment
i am working with ALVR project, which use C++/Rust language.

i will use workaround to solve the current problem(Rust call C API to send ECN UDP packet)
Maybe i can try it, Thank you for your explanation

[stormshield-damiend]

I did a quick study about this support and i think it is doable, i will work on this and submit a PR when done.

[stormshield-damiend]

Little update in teaser mode :

• i now detect the WSARecvMsg function pointer using a dedicated WSAIoctl call as this function is an extension of the network stack
• i have modified recv() and send() function to use socket2 sendmsg() and WSARecvMsg function if detected, if not i fallback to the previous version of the code
• perf client and server still work with the new code
• i am now looking at how to encode and decode control message to enable and use PKTINFO and also ECN

[Ralith]

use socket2 sendmsg() and WSARecvMsg function if detected, if not i fallback to the previous version of the code

Out of curiosity, when do we expect this to fail?

[stormshield-damiend]

use socket2 sendmsg() and WSARecvMsg function if detected, if not i fallback to the previous version of the code

Out of curiosity, when do we expect this to fail?

From what i read, this function was introduced with TCP/IP version 6 extension on Windows XP, what is strange is that nowadays you still need to detect it dynamically event if it seems supported by default since Windows 8.1.

[Ralith]

Huh, that is funny. I'm not sure it's worth the maintenance trouble to maintain a fallback for such old versions of Windows, in any case.

[stormshield-damiend]

Little update :

• new code support ECN and IN[6]_PKTINFO using WSARecvMsg / WSASendMsg and a new wsa_cmsg.rs
• perf client and server work with the new code
• performance seem to be in the same order of magnitude
• tests are currently broken due to new PKTINFO support (i am working on them at the moment)

I plan to send a draft PR as soon as possible

[djc]

Fixed in #1701.