SNMP Tutorial Part 3: Understanding Packet Types and Structure

Part 1 - What is SMNP? | Part 2 - The Management Information Base | Part 3 All 3 parts for easy printing

This article in our series on the Simple Network Management Protocol (SNMP) examines the communication between managers and agents. Basic serial telemetry protocols, like TBOS, are byte oriented with a single byte exchanged to communicate. Expanded serial telemetry protocols, like TABS, are packet oriented with packets of bytes exchanged to communicate. The packets contain header, data and checksum bytes. SNMP is also packet oriented with the following SNMP v1 packets (Protocol Data Units or PDUs) used to communicate:

  1. Get
  2. GetNext
  3. Set
  4. Trap

The manager sends a Get or GetNext to read a variable or variables and the agent's response contains the requested information if managed. The manager sends a Set to change a variable or variables and the agent's response confirms the change if allowed. The agent sends a Trap when a specific event occurs.

SNMP Products:


snmp rtu
32-Point SNMP RTU
rtu power switching
8-port PDU (Power Strip) w/SNMP
security camera rtu
IP camera
w/SNMP
sfp fiber interface for SNMP
SNMP-over-Fiber
RTU
t1 interface for snmp reporting
SNMP-over-T1
RTU

The image below shows the packet formats. Each variable binding contains an identifier, a type and a value (if a Set or response). The agent checks each identifier against its MIB to determine whether the object is managed and changeable (if processing a Set). The manager uses its MIB to display the readable name of the variable and sometimes interpret its value.

SNMP Packet Formats
SNMP Packet Formats

Part 1 - Intro to SNMP | Part 2 - The Management Information Base | Part 3
All 3 parts for easy printing