Abrupt reset sent instead of retransmitting a lost packet

hiren panchasara hiren at strugglingcoder.info
Fri May 13 17:36:40 UTC 2016


https://people.freebsd.org/~hiren/pcaps/tcp_weird_reset.txt
Something we saw in the wild on 10.2ish systems (server and client both).

The most interesting thing can be seen at the end of the file.

3298737767:3298739215 gets lost, client tells us about it via a bunch of
dupacks with SACK info. It SACKs all the outstanding data but this one
missing packet. We (server) never retransmits that missing
packet but rather decide to send a Reset after 0.312582ms. Which somehow
causes client to pause for 75secs. (which might be another issue and not
particularly important for this discussion.)

What could cause this behavior of sending a reset instead of
retransmitting a lost packet? 

Cheers,
Hiren
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