Redundant VIP on F5

The idea here is that they're creating two VIPs: one with a specific IP and port listener, and a second with a generic IP (0.0.0.0) and specific port (80). Because the first VIP is more specific, all traffic destined to that IP and port will flow in that direction by default. If the VIP fails, then the less specific VIP will start answering. Personally I think this config is a bit unnecessary, as you now have a (backup) VIP that'll listen on any IP. I'd question the motivation here. It's far more likely that a backend server will fail before a BIG-IP VIP does, so I'd concentrate on making the actual load balanced services more redundant. Of course with GTM you don't need to do any of this as your "backup" LTM VIPs would be listening on different IPs anyway.