Summary

The three modes of HA deployment and their advantages and disadvantages are summarized in the table below:

Deployment Mode	Configuration Complexity	Physical Complexity	Failover Time	Fallback
One Arm	High (PBR)	Low	Fast <1s	Yes (Intranet & IP SLA)
Parallel Inline	Medium	Medium (VLANS)	Fast <1s	Yes (High Cost Path)
Serial Inline	Medium	Low	Slow 5-15s	Yes (Passthrough)

As a rule of thumb, either One Arm HA configuration or Parallel Inline HA configuration is recommended for Datacenters or Sites that forward a hig volume of traffic to minimize disruption during failover. If a small loss of service is acceptable during a failover, then Serial Inline is a reasonable solution.

Serial Inline HA protects against appliance failure and Parallel Inline HA protects against all failures. In all cases, HA is valuable to preserve the continuity of the APN during a system failure.