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[MX] Inter-chassis stateful synchronization for NAT and stateful firewall flows (MS-MPC, MS-MIC)



Article ID: KB35044 KB Last Updated: 31 Dec 2019Version: 1.0

This article indicates that the default time for stateful synchronization in MX Series routers in Junos OS release 16.1 and later is 180 seconds and longer and that this value is taken into account very strictly for synchronization.

Note: Stateful synchronization replicates session state from the services PICs on the primary chassis to the backup chassis in MX Series routers.



Stateful synchronization synchronizes long-lived sessions [NAT and stateful firewall flows (MS-MPC, MS-MIC)]‚Äč between the primary and the backup MX Series chassis in a high availability pair when sessions have been active on the services PIC for 180 seconds and longer (strictly) starting from Junos OS release 16.1 and later.

Although while configuring inter-chassis stateful synchronization you see the statement set replication-threshold value <60 to 3600>, which indicates that this value is controllable, the system strictly replicates only those sessions that have been active for more than 180 seconds into the backup chassis.

interfaces {
    ms-0/2/0 {
        redundancy-options {
            redundancy-peer {
            redundancy-local {
            routing-instance service-ha;
            inactive: hot-standby;
            replication-threshold 180;  >>>>>>> This value is controllable (60 to 3600).
            replicate-services {



Users are recommended to make a note of this behavior and always use a replication-threshold value of 180 seconds while configuring inter-chassis stateful synchronization.


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