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(usagi-users 04096) Default Router Preference - RFC4191, default route switching



Hi,

I've lately been trying the Default Route Preference on a 2.6.27 kernel, compiling a custom kernel with this option enabled. My intention is to keep established TCP sessions running over a certain prefix/subnet/default route, but when adding another router advertising itself via radvd with a higher preference, having new sessions over this new router. Is/should this be possible with IPv6 (+RFC4191) at all? So far it looks like it works partially the way as intended, but not fully. And I'm wondering if I misunderstood the RFC somehow or if there still might be a bug in the kernel.

For the test setup, in the beginning the host with RFC4191 enabled is using the a router-box with a medium preference prefix / default route for the first connection for a netcat6 connection. Then I added another router with a different subnet and a higher preference to the same local link. The old netcat6 session still used the medium preference prefix / default route as expected and did not break the tcp sessions therefore. Then I started another netcat6: It correctly used the new prefix with a higher preference. However, it still uses the same default route, although I had explicitly set a different AdvRoutePreference for the default route on this second router. Shouldn't the new netcat connection then use the new default route instead (while the old one sticks to the old default route)?

The test setup looks like the following: I have a /48 subnet here with a router establishing the tunnel to the IPv6 PoP. Furthermore, there are two router boxes, each advertising a different /64 subnet from the /48 one via radvd (the ones I've been talking about previously). Their config looks like the following:
======================================
interface br-mesh
{
        AdvDefaultPreference medium;
        AdvSendAdvert on;
        AdvManagedFlag off;
        AdvOtherConfigFlag off;

        prefix 2001:6f8:999:10::1/64
        {
                AdvOnLink on;
                AdvAutonomous on;
                AdvRouterAddr on;
        };
        route ::/0
        {
                AdvRoutePreference medium;
        };
};
=====================================
The second router box has a similar config, except it uses a high preference for the two preference settings and a 2001:6f8:999:11::1 prefix.

The second netcat6 session could be established - though the way to the netcat-server goes over the first router-box (with the right prefix of router-box 2; the way back goes over the right, second router box). The connection is of course being established, as the router-boxes are forwarding the packets no matter if it really is their subnet. I tried to dissallow forwarding from the wrong subnets with ip6tables, but then I just get timeouts or refused connections - the kernel still does not switch to the higher preferenced default route and seems to use the first default route entry in the routing table instead.

Sorry for this a little bit longer mail (hope I was clear enough about what I had expected and what happened instead :) ).

Cheers, Linus