The primary Gateway is used to prevent split brain conditions.

The Gateway has a pre-existing connection to the Active VCE (VCE1 in the “Normal State” diagram above). In a split-brain condition, the Standby VCE (VCE2 in the “Split-brain Condition” diagram above), changes state to Active and establishes a tunnel with the Gateway. The Gateway allows the VCE2 to establish the new tunnel. However, the tunnels are not torn down. The Gateway informs the Edge VCE1 to move to the Standby state. In the 3.3.0 software release, in the Split-brain state, the Standby will also maintain tunnels to the Gateways. Only the LAN interfaces remain blocked (as long as the HA cable is down). As illustrated in the diagram below, the Gateway signals VCE1 to go into Standby mode on the LAN. This will logically prevent the Split-brain scenario from occurring.

Note: The normal failover from Active to Standby in a Split-brain scenario is not the same as the normal failover. It could take a few extra milliseconds/seconds to converge.

split-brain-detection