Heartbeat bandwidth requirements

The heartbeat interface by default carries heartbeat packets and session synchronization packets. When session pickup is enabled, session synchronization traffic will consume a lot of bandwidth on the heartbeat interface. Other heartbeat interface traffic required to synchronize IPsec states, IPsec keys, routing tables, configuration changes, and so on is usually negligible.

The amount of traffic required for session synchronization depends on the connections per second (CPS) that the cluster is processing, since only new sessions (and session table updates) need to be synchronized.

Another factor to consider is that if session pickup is enabled, the traffic on the heartbeat interface surges during a failover or when a unit joins or re-joins the cluster. When one of these events occurs, the entire session table needs to be synchronized. Lower throughput HA heartbeat interfaces may increase failover time if they cannot handle the higher demand during these events.

The amount of heartbeat traffic can also be reduced by:

• Turning off session pickup if it is not needed

• Enabling session-pickup-delay to reduce the number of sessions that are synchronized

• Using the session-sync-dev option to move session synchronization traffic off of the heartbeat link

See Improving session sync performance for more information