Unexpected tcpv6 connection resets since linux 4.4

Unexpected tcpv6 connection resets since linux 4.4

[Andreas Messer]

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Hi there,

i have updated two of my machines in the last weeks to linux 4.4.1 and linux 
4.4.3. It seems that since then i get unexpected TCPv6 connection resets when 
connecting to these machines remotely. The issue occurs with sshd and with a 
http service. /etc/hosts.deny and /etc/hosts.allow are empty on both server 
machines. I'm not so in IPv6 and have no idea whats going on. Please find 
attached a network trace from one of the machines when connecting with ssh (on 
port 23 for debugging). 

Redirects should be accepted according to settings:

root@banana:/proc/sys/net/ipv6# cat conf/wlan0/forwarding 
0
root@banana:/proc/sys/net/ipv6# cat conf/wlan0/accept_redirects 
1
root@banana:/proc/sys/net/ipv6# uname -a
Linux banana 4.4.1-banana #3 SMP Wed Feb 17 23:03:38 CET 2016 x86_64 GNU/Linux

Is there some new network settings or features? My network consists of an 
ethernet/wlan router where subnet of wlan and ethernet are identical.  (forced 
by the router, but was never a problem before). The problem occurs when 
connecting from ethernet machine to wlan machine and when connecting from wlan 
machine to wlan machine. At the moment its not possible to establish a 
connection with these machines using IPv6.

Thanks for help!

Cheers
Andreas

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Re: Unexpected tcpv6 connection resets since linux 4.4

[Cong Wang]

Cc'ing netdev

On Sun, Mar 6, 2016 at 7:10 AM, Andreas Messer <andi@bastelmap.de> wrote:
> Hi there,
>
> i have updated two of my machines in the last weeks to linux 4.4.1 and linux
> 4.4.3. It seems that since then i get unexpected TCPv6 connection resets when
> connecting to these machines remotely. The issue occurs with sshd and with a
> http service. /etc/hosts.deny and /etc/hosts.allow are empty on both server
> machines. I'm not so in IPv6 and have no idea whats going on. Please find
> attached a network trace from one of the machines when connecting with ssh (on
> port 23 for debugging).

Sounds like the problem fixed by the following commit:

commit 9cf7490360bf2c46a16b7525f899e4970c5fc144
Author: Eric Dumazet <edumazet@google.com>
Date:   Tue Feb 2 19:31:12 2016 -0800

    tcp: do not drop syn_recv on all icmp reports


Thanks.


>
> Redirects should be accepted according to settings:
>
> root@banana:/proc/sys/net/ipv6# cat conf/wlan0/forwarding
> 0
> root@banana:/proc/sys/net/ipv6# cat conf/wlan0/accept_redirects
> 1
> root@banana:/proc/sys/net/ipv6# uname -a
> Linux banana 4.4.1-banana #3 SMP Wed Feb 17 23:03:38 CET 2016 x86_64 GNU/Linux
>
> Is there some new network settings or features? My network consists of an
> ethernet/wlan router where subnet of wlan and ethernet are identical.  (forced
> by the router, but was never a problem before). The problem occurs when
> connecting from ethernet machine to wlan machine and when connecting from wlan
> machine to wlan machine. At the moment its not possible to establish a
> connection with these machines using IPv6.
>
> Thanks for help!
>
> Cheers
> Andreas

Re: Unexpected tcpv6 connection resets since linux 4.4

[Andreas Messer]

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On Mon, Mar 7, 2016 at 15:58, Cong Wang <xiyou.wangcong@gmail.com>wrote:
> On Sun, Mar 6, 2016 at 7:10 AM, Andreas Messer <andi@bastelmap.de> wrote:
> > i have updated two of my machines in the last weeks to linux 4.4.1 and
> > linux 4.4.3. It seems that since then i get unexpected TCPv6 connection
> > resets when connecting to these machines remotely. The issue occurs with
> > sshd and with a http service. /etc/hosts.deny and /etc/hosts.allow are
> > empty on both server machines. I'm not so in IPv6 and have no idea whats
> > going on. Please find attached a network trace from one of the machines
> > when connecting with ssh (on port 23 for debugging).
> 
> Sounds like the problem fixed by the following commit:
> 
> commit 9cf7490360bf2c46a16b7525f899e4970c5fc144
> Author: Eric Dumazet <edumazet@google.com>
> Date:   Tue Feb 2 19:31:12 2016 -0800
> 
>     tcp: do not drop syn_recv on all icmp reports

Thanks for the tip. I applied the patch to V4,4,1 and it solved the problem.

Cheers,
Andreas

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