Some builds are set to be mandatory, which means that after a certain date, nodes running the most recent version of fred will no longer connect to older versions except to allow those older versions to obtain and updated version of fred.

• Fixes for known attacks being carried out (see: Frostbite)
• Updates to FNP or crypto systems

• A build must go mandatory before its metadata version becomes the default - Update Over Mandatory uses fblobs, which uses the versioned metadata.