We’ll inform Rene about adding some information about SNMPv3 as well. In the meantime, here is some general information:
SNMPv3 hasn’t changed much from v2 as far as the protocol itself is concerned other than the addition of cryptographic security. Security is the main focus of v3 because security has been the biggest weakness of the protocol since its inception.
Additional changes include new textual conventions, concepts and terminology.
As for the actual configuration of the protocol on Cisco devices, one of the major differences is that you no longer create an SNMP community name, but you create a username, password, and apply authentication and encryption algorithms such as SHA and AES.
So where SNMP commands in v2 would look like this:
Router(config)#snmp-server community StringRW rw SNMPRW
the corresponding command for v3 would be:
Router(config)#snmp-server user snmpManager MGMTSTATIONS v3 auth sha SecurePa55 priv aes 128 Secure3ncrypt access SNMPv3
I hope this has been helpful!