Prefer IPv4 Networking

This workaround will add the -Djava.net.preferIPv4Stack=true JVM argument to the modpack. This can help with networking issues on some systems where Minecraft is unable to authenticate with Mojang's servers.

Enabling Prefer IPv4 Networking

1. Open the FTB App
2. Go to your modpack library
3. Right-click on the modpack you want to enable Prefer IPv4 Networking on and click on settings
4. Scroll down to the Advanced section and enable the Prefer IPv4 network requests option