An Extreme Networks switch has one SNMPv3 engine, identified by its snmpEngineID. The first four octets are fixed to 80:00:07:7C, which represents the Extreme Networks vendor ID. By default, the additional octets for the snmpEngineID are generated from the device MAC address.
Every SNMPv3 engine necessarily maintains two objects: SNMPEngineBoots, which is the number of reboots the agent has experienced and SNMPEngineTime, which is the local time since the engine reboot. The engine has a local copy of these objects and the latestReceivedEngineTime for every authoritative engine it wants to communicate with. Comparing these objects with the values received in messages and then applying certain rules to decide upon the message validity accomplish protection against message delay or message replay.
In a SummitStack, the MAC address chosen for the snmpEngineID is the configured stack MAC address.