There are two mode in which you can use IPv6 in mIRC:
- Local mode - Using /server -6
- Global mode - Using the option (alt + o > Connect > options > ports button > Enable IPv6 support and prioritize IPv6 over IPv4 connections)
When you use /server -6, mIRC binds to an IPv6 adapter, this overrides the Global mode for that connection only.
This means you cannot use IPv4 on that connection, even /dns -4 will not work, this is because IPv4 is simply disabled.
In this mode, using /sockopen with an host that resolve to an IPv4 IP address will not work as well.
If you want to use IPv6 while still having IPv4 support, you must use the Global mode, see below.
Remember, this option can be enabled/disabled at alt + o > Connect > options > ports button > Enable IPv6 support and prioritize IPv6 over IPv4 connections.
In this mode, IPv6 has priority but IPv4 is not disabled.
This mode is recommended. Use /server -6 only if you want to disable IPv4 for anything happening from that connection.