Consider two SSR's that are connected to each other and managed by Mist. SSR1 has LAN1 network connected to its LAN interface while SSR2 has LAN2.

Communication works only from LAN1 to LAN2 even through there is application policy defined to allow the traffic.

In this scenario define two application policies. One with source set to LAN1 and destination set to LAN2 and other policy with source set to LAN2 and destination set to LAN1. The two policies need to be applied on both the SSR''s.

This is because the direction of traffic where the session is initiated matters. If there is only one application policy with source LAN1 and destination LAN2, it will only allow communication for traffic initiated from LAN1 to LAN2.