SNMPv3 requires an SNMP agent to define a unique "engine ID" in order to respond to SNMPv3requests. This ID will normally be determined automatically, using two reasonably non-predictable values:
a (pseudo-)random number and
the current time in seconds.
This is the recommended approach.
However the capacity exists to define the engineID in other ways:
engineID STRING
specifies that the engineID should be built from the given text STRING.
engineIDType 1|2|3
specifies that the engineID should be built from the IPv4 address (1), IPv6 address (2) or MAC address (3). Note that changing the IP address (or switching the network interface card) may cause problems.
engineIDNic INTERFACE
defines which interface to use when determining the MAC address. If engineID Type 3 is not specified, then this directive has no effect.
The default is to use eth0.