BEP 29: packets with unrecognized IDs

[povilasb]

http://www.bittorrent.org/beps/bep_0029.html doesn't specify how one should handle packets whose connection ID is not known for us. For example,

1. we receive Fin(connection_id=1234) packet.
2. We have never sent or received Syn(connection_id=1234)
3. What do we do with the packet?

• ignore it?
• send Reset packet back?

Thanks :)

[ssiloti]

In theory a reset packet should be sent in response to a packet with an unknown connection ID, but libtorrent at least ignores such packets. I assume this was done to avoid amplification attacks.

[the8472]

RST packets should be small, so there shouldn't be any amplification as long as you verify that you're responding to something that has the minimum plausible packet size and rate-limit them. Sure, there's reflections, but those are unavoidable and you get them with TCP or properly-crafted requests too.

[arvidn]

as a separate note, you shouldn't send an RST back to an unrecognised RST packet.

[povilasb]

Okey dokes, thanks guys, before closing this issue I'll try to do a PR for BEP 29 that specifies this behavior when I'm done with my work on uTP - that might take about 2 weeks though :)