High availability requires Gratuitous Address Resolution Protocol (GARP) support on the connected network elements. When the primary Avaya SBC fails over, the secondary Avaya SBC broadcasts a GARP message to announce that the secondary Avaya SBC is now receiving requests. The GARP message announces that a new MAC address is associated with the Avaya SBC IP address. Devices that do not support GARP must be on a different subnet with a GARP-aware router or L3 switch to avoid direct communication. For example, to handle GARP, branch gateways, Medpro, Crossfire, and some PBXs/IVRs must be deployed in a different network from Avaya SBC, with a router or L3 switch. If you do not put the Avaya SBC interfaces on a different subnet, after failover, active calls will have a one-way audio. Devices that do not support GARP continue sending calls to the original primary Avaya SBC.

All IP addresses configured on the Network Configuration screen are shared between both HA devices in HA deployment mode. The HA devices are also configured with private, default IPs that are used to replicate signaling and media data between each other. The configured interfaces are inoperative on the standby or secondary device until the device becomes active or primary. When the devices failover, the active device sends a GARP message to update the ARP tables of the neighboring HA device to begin receiving traffic.