linux-kernel - Re: IPv6 and private net with masquerading not working correctly

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Message-ID: <562C8A4F.1030302@wiesinger.com>
Date:	Sun, 25 Oct 2015 08:52:47 +0100
From:	Gerhard Wiesinger <lists@...singer.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	netfilter-devel@...r.kernel.org
Cc:	Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: IPv6 and private net with masquerading not working correctly

Any update on this issue?

Thank you.

Ciao,
Gerhard

On 10.08.2015 19:39, Cong Wang wrote:
> (Cc'ing netdev and netfilter-devel)
>
> On Fri, Aug 7, 2015 at 6:00 AM, Gerhard Wiesinger <lists@...singer.com> wrote:
>> On 06.08.2015 20:43, Gerhard Wiesinger wrote:
>>> Hello,
>>>
>>> I'm having the following problem with IPv6 and a private internal LAN
>>> which will be masqueraded to the public internet (I don't want to have
>>> public IPs in the LAN because of some static IPs and tracking) . Rules are
>>> generated by shorewall.
>>>
>>> Problem is that ICMP6 packets source address is not translated by the
>>> kernel on the reply when MTU has to be discovered because of too big packets
>>> and limited MTU capabilities on the path (happens also on tcp6 which works
>>> thereofore not correctly).
>>>
>>> # From an internal host on net fd00:1234:5678::/64
>>> ping6 -s 2000 2a02:1234:5678:7::2
>>>
>>> /etc/shorewall6/masq
>>> EXT_IF                   fc00::/7
>>>
>>> ip6tables rule:
>>> MASQUERADE  all      *      *       fc00::/7             ::/0
>>>
>>> # Internal interface
>>> IP6 fd00:1234:5678::9 > 2a02:1234:5678:7::2: frag (0|1432) ICMP6, echo
>>> request, seq 1, length 1432
>>> IP6 fd00:1234:5678::9 > 2a02:1234:5678:7::2: frag (1432|576)
>>> IP6 2a02:1234:5678:9abc::115 > fd00:1234:5678::9: ICMP6, packet too big,
>>> mtu 1440, length 1240
>>>
>>> # External interface
>>> IP6 2001:1234:5678:9abc::1 > 2a02:1234:5678:7::2: frag (0|1432) ICMP6,
>>> echo request, seq 1, length 1432
>>> IP6 2001:1234:5678:9abc::1 > 2a02:1234:5678:7::2: frag (1432|576)
>>> IP6 2a02:1234:5678:9abc::115 > 2001:1234:5678:9abc::1: ICMP6, packet too
>>> big, mtu 1440, length 1240
>>>
>>> Looks to me like a a major kernel bug.
>>> Kernel version is: 4.1.3-201.fc22.x86_64 from Fedora 22
>>>
>>> Any ideas?
>>>
>> Any comments?
>>
>> Ciao,
>> Gerhard
>>
>> --
>> http://www.wiesinger.com/
>>
>>
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