Subject: Fw: [Bug 111041] New: random openssh connection failure during connection to server

From: Stephen Hemminger <[email-masked]>
Date: Wed, 20 Jan 2016 09:55:51 -0800

Begin forwarded message:

Date: Wed, 20 Jan 2016 10:14:17 +0000
From: "[email-masked]" <[email-masked]>
To: "[email-masked]" <[email-masked]>
Subject: [Bug 111041] New: random openssh connection failure during connection to server

https://urldefense.proofpoint.com/v2/url?u=https-3A__bugzilla.kernel.org_show-5Fbug.cgi-3Fid-3D111041&d=CwICaQ&c=IL_XqQWOjubgfqINi2jTzg&r=q_lvUiVm1uM6QEw9TPH-6jiV__hsrE6xXUAtATPE9x0&m=Jk3RwPbncUW6RyLfcTeu44MAZ0LFZm_HFxRIcPFJaEs&s=Jrbgmvu1hu8KrQlA3sTLXDCgTkW3xtWM9UuXUmMnf9M&e= 

            Bug ID: 111041
           Summary: random openssh connection failure during connection to
                    server
           Product: Networking
           Version: 2.5
    Kernel Version: 4.4.0
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: IPV4
          Assignee: [email-masked]
          Reporter: [email-masked]
        Regression: No

It's sometimes impossible to connect to a server running Gentoo Linux with
kernel 4.4 using ssh. The problem is only the connection, it fails a few times
but then it goes fine and ssh works as expected.

OpenSSH_7.1p2-hpn14v10, OpenSSL 1.0.2e 3 Dec 2015
debug1: Reading configuration data /etc/ssh/ssh_config
debug2: ssh_connect: needpriv 0
debug1: Connecting to 10.0.0.5 [10.0.0.5] port 22.
debug1: Connection established.
debug1: Enabling compatibility mode for protocol 2.0
write: Connection reset by peer

Or alternatively it fails with "ssh_exchange_identification: read: Connection
reset by peer".

We were able to reproduce this problem with random clients, Gentoo, Ubuntu,
Debian, random kernels. It's interesting that only 1 client doesn't have a
problem to connect to the server - a system with Gentoo Linux Hardened 4.1
(using the same openssh version).

The server is a Supermicro X10DRW, Intel PCI-Express Gigabit Ethernet (igb)
networking. Two ethernet ports were connected to bond and that to a bridge for
xen. I've also tried without bond and without any iptables rules, it didn't
help. This setup works without any modification on kernel 4.1.15.

A Gentoo forum post: https://urldefense.proofpoint.com/v2/url?u=https-3A__forums.gentoo.org_viewtopic.php-3Fp-3D7868744&d=CwICaQ&c=IL_XqQWOjubgfqINi2jTzg&r=q_lvUiVm1uM6QEw9TPH-6jiV__hsrE6xXUAtATPE9x0&m=Jk3RwPbncUW6RyLfcTeu44MAZ0LFZm_HFxRIcPFJaEs&s=SuurWudhyHYuvvaWUtAMY_Yihv7qKIBzXVesBCNhj04&e= 

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