When using the setup utility to configure a redundant pair, you are asked to provide a "Failover Peer IP". Which address is this.

While it might be an address on the management network, the critical part is that it's of the other system, not just specifically the management network, and it's for failover, not just general management.

When configuring a redundant BIG-IP pair using the setup utility, the "Failover Peer IP" explicitly asks for an IP address of the other system in the redundant pair. This address is used by the local device to communicate with its partner for purposes like sending and receiving failover heartbeat messages and determining the health and state of the peer device.

This describes an address on the current system used to listen for failover messages, but the Failover Peer IP refers to the address of the partner system.

This describes an address on the current system used to initiate mirroring and network failover heartbeat messages, but the Failover Peer IP refers to the destination address on the partner system.