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kern/51753: tcp SACK causes SSH disconnects
>Synopsis: tcp SACK causes SSH disconnects
>Arrival-Date: Fri Dec 30 09:50:00 +0000 2016
>Originator: Brian Marcotte
Public Access Networks, Corp.
NetBSD trinity.nyc.access.net 7.0.2 NetBSD 7.0.2 (PANIX-XEN-STD) #1: Mon Nov 21 12:57:01 EST 2016 root%juggler.panix.com@localhost:/misc/obj/misc/devel/netbsd/7.0.2/src/sys/arch/i386/compile/PANIX-XEN-STD i386
Ever since we started upgrading to NetBSD-7, we've been getting weird
client: Corrupted MAC on input. Disconnecting: Packet corrupt
server: panix5 sshd: error: Received disconnect from x.x.x.x:
2: Packet corrupt
It turns out, just replacing the kernel only and keeping the NetBSD-6
userland will cause the problem to show up. SSH client/server versions
don't appear to matter.
I traced this down to a change in the kernel between 2013-Nov-12 and
2013-Nov-13. I suspect the problem is in one of these files commited
on that day:
The above commits added "cubic" congestion control but also moved SACK
In our case, certain types of terminal output can cause the problem.
I can now get it to happen somewhat reliably by compiling a NetBSD
It may be that there must be some other network problem for this to
happen as I've not seen anyone else report this problem.
I don't know how to fix it but turning off SACK seems to be a
sysctl -w net.inet.tcp.sack.enable=0
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