bilbo opened the ticket and wrote:

On my system, I have IPv6 support (debian unstable), however due to ISP not supporting IPv6, any IPv6 packets sent to internet basically end up in /dev/null

I started a dedicated server using "./openttd -D" and it seems not to appear in the master list and on console I see this:

dbg: [net] [udp] advertising to master server
dbg: [net] [udp] sendto([master.openttd.org]:3978 (IPv6)) failed with: 101

Seems like it is using IPv6 in the attempts to communicate with master server.

Peeking into sources reveals this call reponsible for communication with master server:

void NetworkUDPAdvertiseThread(void *pntr)
....
NetworkAddress out_addr(NETWORK_MASTER_SERVER_HOST, NETWORK_MASTER_SERVER_PORT);

Looking at definition of NetworkAddress constructor:
NetworkAddress(const char *hostname = "", uint16 port = 0, int family = AF_UNSPEC)

So there seems to be no switch whether to use IPv4 or IPv6 in the attempts to communicate with master server. In my case the "guess" parameter of AF_UNSPEC probably ended up with IPv6 being used instead of IPv4.

I think there should be switch/settings whether openttd will use IPv4, IPv6 or autodetect for all network communication - as in some situations, both IPv4 and IPv6 protocols seems to be available (my machine have IPv4 and IPv6 address), DNS for master.openttd.org will return both A and AAAA records, but ISP tosses IPv6 packets away on their nearest router (which openttd have no chance knowing)

Reported version: trunk
Operating system: All

This issue was imported from FlySpray: https://bugs.openttd.org/task/2822