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    SubjectRe: netfilter: marking IPv6 packets sends them to the wrong interface
    Am 24.01.2011 18:02, schrieb Mario 'BitKoenig' Holbe:
    > On Mon, Jan 24, 2011 at 05:10:50PM +0100, Patrick McHardy wrote:
    >>> Yes, disabling the ip6_route_me_harder() call in ip6t_mangle_out()
    >>> results in the advertisements being transmitted on the correct
    >>> interfaces
    >> Thanks. The problem appears to be that ip6_route_me_harder()
    >> only uses the socket's oif for the route lookup when the
    >> socket is bound to an interface, but radvd uses IPV6_PKTINFO
    >> to specify the outgoing interface.
    >> I guess netfilter shouldn't be overriding IPV6_PKTINFO, but
    >> we unfortunately have neither an indication of this nor the
    >> original route lookup keys available at the time the packet
    >> is rerouted.
    > Mh, I'm not sure, but I guess an indication of netfilter not overriding
    > IPV6_PKTINFO could be the fact that the source address does not
    > change...

    No, ip6_route_me_harder() only attaches a new route to the packet,
    the packets contents are not changed.

    > From my 1st mail:
    > | # ip6tables -t mangle -A OUTPUT -o eth0 -j MARK --set-mark 1
    > | # /etc/init.d/radvd start
    > | -> eth0: <no traffic>
    > | -> eth1: fe80::2a0:c9ff:fee6:90ce > ff02::1: prefix 2001:6f8:90c:10::/64
    > | -> eth1: fe80::2d0:b7ff:fe06:6b36 > ff02::1: prefix 2001:6f8:90c:12::/64
    > fe80::2d0:b7ff:fe06:6b36 is the link-local address of eth0 set by radvd
    > in IPV6_PKTINFO as well. This, of course, is no guarantee for
    > ipi6_ifindex not being changed, but I believe if something would have
    > changed it, it would also have changed ipi6_addr.

    No, what is happening is that radvd sends the packet with a specified
    ifindex using IPV6_PKTINFO. The mangle table notices that the mark
    changes and calls ip6_route_me_harder(), which performs a new route
    lookup without taking the specified oif into account. It therefore
    chooses the first of your two routes and sends the packet out eth1.

     \ /
      Last update: 2011-01-24 18:53    [W:0.021 / U:1.112 seconds]
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