UDP support? about proxy-protocol HOT 2 CLOSED

Hi @ronf, for all the reasons you seem to have discovered, proxy protocol isn't really well suited (or easily suited) to UDP. Due to datagram packet size limitations, it's not necessarily safe to just add a header to every packet unless the application protocol is guaranteed to leave enough room.

One possibility would be to send a packet that contains the full proxy protocol header (v2 + TLV can be a few hundred bytes) and subsequent application packets could simply reference the header (e.g. by hash), assuming that each source is cached on the receiver side. I don't think something like that could be made generic enough to include in this library, especially without inclusion in the proxy protocol spec, but it could work for your situation.

Hope that helps, feel free to reopen if you have any more questions or ideas.

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Thanks for getting back to me. I agree with the concerns you mentioned around length. Adding such a header in every packet would probably not exceed the max UDP datagram size, but it could lead to IP fragmentation if the original UDP packets were already close to the MTU in size, and having every packet fragmented is far from ideal.

There's also an ordering and packet loss concern with the "hash" approach, if the initial packet with the full header is dropped or if it arrives out of order and the receiver gets a packet with the hash in it before the one with the full header.

To be clear, my original question was to try and get clarity on the current proxy protocol v2 spec and not to ask for something new to be implemented. It seems like maybe there isn't an implementation that addresses these issues, though, despite to spec mentioning UDP as one of the options.

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