Re: kern/55800: Data transfers stall when SACK is enabled

[Frank Kardel <kardel%netbsd.org@localhost>]

The following reply was made to PR kern/55800; it has been noted by GNATS.

From: Frank Kardel <kardel%netbsd.org@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/55800: Data transfers stall when SACK is enabled
Date: Tue, 22 Nov 2022 10:13:31 +0100

 Another data point:
 
 The problem still exists in 9.99.100 (and likely thereafter).
 
 After a missed sequence of 17k bytes an ACK for the last successful 
 segment before the ole is being sent by the receiver including SACK for 
 segments received past the missed segments.
 
 These ACKs(+SACKS) reach the sender and the sender resumes sending for 
 about 4-5k and then stalls. (traces are available)
 
 Disabling SACK helps as already observed.
 
 Frank
 
 
 On 11/12/20 08:10, Michael van Elst wrote:
 > The following reply was made to PR kern/55800; it has been noted by GNATS.
 >
 > From: mlelstv%serpens.de@localhost (Michael van Elst)
 > To: gnats-bugs%netbsd.org@localhost
 > Cc:
 > Subject: Re: kern/55800: Data transfers stall when SACK is enabled
 > Date: Thu, 12 Nov 2020 07:08:01 -0000 (UTC)
 >
 >   kim%netbsd.org@localhost (Kimmo Suominen) writes:
 >   
 >   > Sadly this also happens if both ends are running 9.1.  The transfer
 >   > stalled after about 1 GB of data having been transferred.  After
 >   > disabling SACK (on the local end) and restarting the transfer, it
 >   > completed without any stalling (transferring another 9 GB of data).
 >   
 >   The tcpdump shows that some packet from the sender gets lost and
 >   the receiver SACKs subsequent segments. The sender then stops.
 >   
 >   After an hour, the receiver pushes an ACK (still only for the
 >   received segments), but the sender continues sending packets of the
 >   stream as if nothing has happened. No retry packet is received
 >   in the sequence.
 >   
 >   Is there anything between sender and receiver? firewall? packet filter
 >   (also on either machine) that could drop the retry packets ?
 >   
 >   --
 >   --
 >                                   Michael van Elst
 >   Internet: mlelstv%serpens.de@localhost
 >                                   "A potential Snark may lurk in every tree."
 >