2011-10-17

IP6IP6 tunnel - routing issue

Mobile IPv6 implementation in Linux is using different metric values for each Care-of Addresses, when creates or modifies default routes. This cause, that all of the packets are goes out on the interface which has lower metric value, independently from the tunnel interface. In practice it cause that the packets which are routed into ip6tnl2 are goes out on eth1, instead of the setup, which binds ip6tnl2 to eth2.



You could test it with the attached test script.

We found the following issue:



Here the iteration goes until the metric is equal to the specified one. If you look the calling environment, you should see, that this metric value is the metric of the first route info entry:



We have two totally same route entries, where only the interfaces and the metric values are different:

default via fe80::20c:29ff:fe3b:4d16 dev eth1  proto ra  metric 1023  mtu 1500 advmss 1440 hoplimit 0
default via fe80::20c:29ff:fe3b:4d20 dev eth2  proto ra  metric 1053  mtu 1500 advmss 1440 hoplimit 0

In this case, the above loop, will call find_match only once, for eth1. If it happens, the find_match funcin, couldn't find eth2, which belongs to ip6tnl2, and returns with eth1.

The attached patch, introduces a new route lookup flag: RT6_LOOKUP_F_IP6TUNNEL. It is passed step-by-step to find_rr_leaf, and it will ignore the metric condition in the loop, if this flag has been enabled.

The ip6ip6-metric-fix.patch contains the fix for 2.6.35.14. We had to edit the definition of ip6_route_output, and the ip6ip6-metric-stuff.patch contains the modification of calling this at any other occurrences.


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