Re: IPv6 and private net with masquerading not working correctly

[Gerhard Wiesinger <lists@wiesinger.com>]

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

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