My sister got Minecraft yesterday and we're unable to join each others' LAN servers. We're on the same Wi-Fi router, neither of us have firewalls blocking Java and have updated to the most recent version, we're both on the same version of Minecraft, etc. The other troubleshooting articles/questions I've seen are aimed at Windows users– both of us are on OS X El Capitan. Thank you in advance for your help!
Minecraft – Help with Minecraft LAN Server on Mac
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Best Answer
In the launcher, go into the "Installations" tab. Choose a profile to patch. This method won't disrupt your game in any way, but if you're worried about breaking something, create a new installation.
Open the "More Options" panel, and paste the following text at the beginning of the "JVM Arguments" text field:
Mac is simply using iPv6 instead of iPv4 to try to connect to LAN worlds. The above text fixes that and forces it to prefer iPv4.