Version 4.1 - 3.9 SNMP
SNMP is Simple Network Management Protocol. But there are books written about it - it's anything but simple if you've ever looked at a MIB. Cisco's page on SNMP is a good reference for this section.
Know your SNMP versions:
SNMPv1
SNMPv2c
SNMPv3
SNMPv3 adds message integrity, authentication and encryption. For SNMPv3 know the difference between NoAuthNoPriv | authNoPriv | authPriv . Know your RW and RO communities. Know the difference between traps and informs (traps are sent - informs are acknowledged traps). Note that SNMP operates at the Application Layer of the OSI mode.
Seven SNMP PDU types:
GetRequest
SetRequest
GetNextRequest
GetBulkRequest
Response
Trap
InformRequest
Note that most of these use UDP port 161 (on the agent) except for Traps and InformRequests - which use UDP port 162.
Versions 1 and 2c are subject to packet sniffing (or guessing) since it uses community strings that are sent over the network as clear text. Although Version 3 is "more" secure, it can be subject to brute force and dictionary attacks.
If you've worked on a network before, you've probably set up snmp a million times on a million devices. And think about the address where you sent this information. The routers and switches were the snmp agents and the address you sent this stuff to was the SNMP manager (NMS). Think about how this plays out in access-lists - that's where you might see this material in a question. And know MIBs and OIDs. Management Information Base - Object Identifiers. Everything in the device has a specific OID which travels down the MIB structure to identify it specifically. What you see in your NMS is actually a visual display of the devices and the MIBs with the response to pings and polls (along with trap information) displayed as the "alerts" and "status" of devices. If you've worked with various NMS, this section should not be a problem.