PIC Resiliency: Inter-chassis high availability provides stateful redundancy

Junos OS supports stateful high availability (HA) to replicate flow states on an active MS-MPC or MS-MIC service card to a standby MS-MPC or MS-MIC service card on a different chassis. This enables the preservation of the state of the existing flows in case of a planned or unplanned switchover. Services to be synchronized statefully include: 

•  Stateful firewall 
• NAT (NAPT44 and APP only) 

Both IPv4 and IPv6 sessions are synchronized.

Synchronization occurs for long-lived flows as defined by a configurable synchronization threshold.