Each firewall needs a dedicated interface for the HA3 link.
The PA-7000 Series, PA-5400 Series, PA-3400 Series, and PA-3200
Series firewalls use the HSCI port for HA3. The PA-5200 Series firewalls
can use the HSCI port for HA3 or you can configure aggregate interfaces
on the dataplane ports for HA3 for redundancy. On the remaining
platforms, you can configure aggregate interfaces on dataplane ports
as the HA3 link for redundancy.