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Understanding Chassis Cluster Redundancy Group Failover

Chassis cluster employs a number of highly efficient failover mechanisms that promote high availability to increase your system's overall reliability and productivity.

A redundancy group is a collection of objects that fail over as a group. Each redundancy group monitors a set of objects (physical interfaces), and each monitored object is assigned a weight. Each redundancy group has an initial threshold of 255. When a monitored object fails, the weight of the object is subtracted from the threshold value of the redundancy group. When the threshold value reaches zero, the redundancy group fails over to the other node. As a result, all the objects associated with the redundancy group fail over as well. Graceful restart of the routing protocols enables the SRX Series device to minimize traffic disruption during a failover.

Back-to-back failovers of a redundancy group in a short interval can cause the cluster to exhibit unpredictable behavior. To prevent such unpredictable behavior, configure a dampening time between failovers. On failover, the previous primary node of a redundancy group moves to the secondary-hold state and stays in the secondary-hold state until the hold-down interval expires. After the hold-down interval expires, the previous primary node moves to the secondary state. If a failure occurs on the new primary node during the hold-down interval, the system fails over immediately and overrides the hold-down interval.

The default dampening time for a redundancy group 0 is 300 seconds (5 minutes) and is configurable to up to 1800 seconds with the hold-down-interval statement. For some configurations, such as those with a large number of routes or logical interfaces, the default interval or the user-configured interval might not be sufficient. In such cases, the system automatically extends the dampening time in increments of 60 seconds until the system is ready for failover.

Redundancy groups x (redundancy groups numbered 1 through 128) have a default dampening time of 1 second, with a range from 0 through 1800 seconds.

The hold-down interval affects manual failovers, as well as automatic failovers associated with monitoring failures.

On SRX Series devices, chassis cluster failover performance is optimized to scale with more logical interfaces. Previously, during redundancy group failover, Generic Attribute Registration Protocol (GARP) is sent by the Juniper Services Redundancy Protocol (jsrpd) process running in the Routing Engine on each logical interface to steer the traffic to the appropriate node. With logical interface scaling, the Routing Engine becomes the checkpoint and GARP is directly sent from the Services Processing Unit (SPU).

Note: On SRX5400, SRX5600 and SRX5800 devices in chassis cluster mode with next-generation SPCs installed on all slots, occasionally during the device bring-up, when cluster nodes are rebooted with delay of less than 60 seconds, it might encounter RG1+ failover.