Currently I am connected to Internet over IPv4, I am using tunnel from sixxs.net and I have got subnet and one of IPv6 assigned to my eth0 interface.
So, eth0 has IPv4 and IPv6:
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000 link/ether 00:02:XX:XX:61:36 brd ff:ff:ff:ff:ff:ff inet XXX.XXX.0.22/24 brd XXX.XXX.0.255 scope global eth0 inet6 2a01:XXXX:XXXX::1/64 scope global valid_lft forever preferred_lft forever
When I am trying to connect to some eg. website which is IPv6 ready, it is fine, IPv6 is preferred, but If something happen and it's IPv6 is not available I would like to have fall-back to IPv4. Is that possible?
Or is possible to temporary force user IPv4 instead of IPv6 even if program does not support (eg. by -4 option)?