Loss recovery at tail

Michael Tuexen tuexen at freebsd.org
Sat Nov 19 13:51:02 UTC 2016

> On 19 Nov 2016, at 00:13, hiren panchasara <hiren at strugglingcoder.info> wrote:
> On 11/18/16 at 09:20P, Michael Tuexen wrote:
>> Dear all,
>> in the last telco we discussed the behaviour when that last N packets are dropped.
>> It was mentioned that multiple retransmission timers where used to recover.
>> I wrote a packetdrill script which
>> * Get the cwnd to 30 segments
>> * Sends 30 segments, which all get lost
>> * Observe how the 30 dropped segments are retransmitted.
>> It uses only a single timeout as one would expect.
>> So this script does NOT reproduce the problem, but I'm attaching it such that
>> you can see how the stack behaves.
>> Tested with FreeBSD head r308802.
> Thanks for testing.
> https://reviews.freebsd.org/D8556 was the issue detecting a valid
> RTO as bad and resetting snd_nxt to snd_max (instead of snd_una as done by
> valid RTO) causing us to not trigger retransmit of missed packets but
> wait for RTO for all of lost packets.
Ahh, I see. Thanks for the pointer.

Best regards
> Cheers,
> Hiren

More information about the freebsd-transport mailing list