Understanding Chassis Cluster Redundancy Group 0: Routing Engines

When you initialize a device in chassis cluster mode, the system creates a redundancy group referred to in this document as redundancy group 0. Redundancy group 0 manages the primacy and failover between the Routing Engines on each node of the cluster. As is the case for all redundancy groups, redundancy group 0 can be primary on only one node at a time. The node on which redundancy group 0 is primary determines which Routing Engine is active in the cluster. A node is considered the primary node of the cluster if its Routing Engine is the active one.

The redundancy group 0 configuration specifies the priority for each node. Below is how redundancy group 0 primacy is determined. Note that the three seconds value is the interval if the default heartbeat-threshold and heartbeat-interval values are used.

• The node that comes up first (at least three seconds prior to the other node) is the primary node.
• If both nodes come up at the same time (or within three seconds of each other):
  • The node with the higher configured priority is the primary node.
  • If there is a tie (either because the same value was configured or because default settings were used), the node with the lower node ID (node 0) is the primary node.

The above priority scheme applies to redundancy groups x (redundancy groups numbered 1 through 128) as well, provided preempt is not configured.

You cannot enable preemption for redundancy group 0. If you want to change the primary node for redundancy group 0, you must do a manual failover.

Caution: Be cautious and judicious in your use of redundancy group 0 manual failovers. A redundancy group 0 failover implies a Routing Engine failover, in which case all processes running on the primary node are killed and then spawned on the new master Routing Engine. This failover could result in loss of state, such as routing state, and degrade performance by introducing system churn.

Related Topics

• JUNOS Software Feature Support Reference for SRX Series and J Series Devices
• Understanding Chassis Cluster Redundancy Groups 1 Through 128
• Example: Configuring Chassis Cluster Redundancy Groups (CLI)
• Verifying Chassis Cluster Redundancy Group Status
• Understanding Chassis Cluster Redundancy Group Failover
• Understanding Chassis Cluster Redundant Ethernet Interfaces
• Understanding Chassis Cluster Formation