Joep.
Did you disable ipV6 in Yast-Network Settings? That’s not enough, you also need to add
ipv6-disable=1
to the boot options line, or, to make it persistent, add it to the boot options line in “/boot/grub/menu.lst”
Do I understand well, that with DNS’s configured manually in Yast, all works as it should? I would say then, that with ipv6 completely disabled (see above), it’s in the router’s configs.
Prettig weekend