We have set up an IPv6 only network. To get IPv4 connectivity between
two machines I used an IPv4 over IPv6 gif tunnel. Both machines run
route6d, one listens only the other advertises routes. I noticed 
something strange. After initial tunnel setup I lost all IPv6 
connectivity (from the machine with the listening route6d). 

Looking at the routing table it seemed the machine had received
IPv6 route updates from the other side of the tunnel, i.e. over
IPv4. The machine effectively had all its IPv6 routes pointing
over the IPv4 tunnel now, instead of over the IPv6 Ethernet.

So, it seems to me that route6d assumes that when it receives
route updates over an interface, that interface provides connectivity
for both IPv4 and IPv6 (and/or the sending route6d makes a similar
assumption). I haven't tried whether route6d behaves in a similar
way with 2 Ethernet interfaces; one IPv6 only, and one IPv4 only.

Now, this particular problem was easy to solve by telling route6d not
to advertise routes over the tunnel. However, my feeling is this
should not be necessary and that route6d should only advertise routes
over interfaces that actually provide connectivity for the address
family of the route...

Any comments before I send-pr this?

Feico.