Ubuntu 16.04.5 with kernel 4.4 used to work as intended: IPv4 is default. Since changing to kernel (hwe) 4.15, it uses IPv6 as default.
It has IPv6 available via Tunnelbroker, broadcasted by the router.
It is now defaulting to IPv6: curl ifconfig.co
returns the machine's IPv6. Only curl -4 ifconfig.co
returns the desired IPv4 address. (curl -6 ifconfig.co
as expected returns IPv6)
$ ip rule list
0: from all lookup local
32766: from all lookup main
32767: from all lookup default
$ ip -6 rule list
0: from all lookup local
32766: from all lookup main
$ ip route list
default via 192.168.1.1 dev eth0
192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.x
$ ip -6 route list
2001:470:x:999::9999:f6a dev eth0 proto kernel metric 256 pref medium
2001:470:x:999::/64 dev eth0 proto kernel metric 256 expires 42905sec pref medium
fe80::/64 dev eth0 proto kernel metric 256 pref medium
default via fe80::2ac6:8eff:fe65:d117 dev eth0 proto ra metric 1024 expires 1505sec hoplimit 64 pref medium
PS: Some providers still report IPv4, for example curl ipinfo.io/ip
. I've used ifconfig.co for a long time, so I am not sure if they changed their setup (less likely) or the kernel upgrade makes Ubuntu prefer IPv6.
How do I find out what is causing IPv6 to be preferred?