In Palo Alto Active/Active is not at all about capacity, so you won't find it mentioned in the documentation. The use cases are just two: Asymmetrical routing - there are two active paths and source and reply traffic can appear on different links. The A/A setup allows the sessions to still be matched and processed by the original firewall. Dynamic routing protocol load balancing - There are two paths that traffic could take through the firewalls and that path is selected by routing preferences in dynamic routing protocols outside the PA firewall. The inactive path interfaces must remain up for the dynamic peers to maintain their routing tables. In an active/passive design the passive firewall links are down and the peers on the secondary path cannot remain up. See the discussion in the Active/Active Tech note for more details. Configuring Active/Active HA PAN-OS 4.0
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