New blog article: How to synchronize Gig Performer's tempo to an external MIDI clock or Link-enabled products - Gig Performer®
How do you synchronize Gig Performer’s tempo 
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Other:
[1] Gig Performer and Live virtual MIDI port sync → LINK
[2] How to sync the transports between Cubase and GP without syncing the tempo → LINK
[3] About routed networks: Ableton Link uses multicast port 20808, so you need a router that’s capable of doing multicast. → LINK