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SNMP Overview

Simple Network Management Protocol (SNMP) is a Management Protocol most used in network management systems. More than 70% of the world's network equipment supports SNMP, and as it has a long history, it is easy to develop and verify with various tools and libraries that have already been verified.

 

On the other hand, the simple structure of GET, SET, and NOTIFICATION is not easy to standardize, and it is difficult to implement various OAM functions. There are many standard MIBs defined by IETF(RFC xxxx), and large equipment manufacturers basically support them, but most of the MIBs required for operation are supported as private MIBs, and the main functions are often vendor specific.

 

As a result, Service Providers requested a standardized operation plan, which became the background for NETCONF and others. Nevertheless, since SNMP is still the most widely used protocol, so it is essential to understand the management system.


The history of SNMP

As the Internet based on TCP/IP appeared in the 1980s, standardization of management funtion was required, and SNMP was introduced by IETF. They defined a simple operation such as Get, Set, and Trap, but in reality, it was a protocol that required a fairly complex implementation, and there were many restrictions on operation. Anyway, the concept of SNMP first appeared in RFC1067 in 1988. 

# RFC1067 (A Simple Network Management Protocol)

  

SNMP Version 1 is fully defined in RFC 1157 (1988). It is a standard in which all basic concepts of SNMP are defined.

Since then, SNMP Version 2 has the current framework as RFC 1441 and others appeared in the 1990s.

SNMP Version 3 appears in the 2000s as the demand for security increases. About ten years ago, there was no problem when only supporting SNMPv2c, but recently SNMPv3 is mandatory.


SNMP Operation

SNMP consists of communication between Manager and Agent. Manager performs the function that goes up to management system such as NMS or EMS. It is the subject of Get, Set and recipient of Notification (Trap). Agent is implemented in Network Device and performs the function to respond to the Manager's Get and Set Operation. When an event occurs, related information is delivered to the manager through a trap.

 

  • Get: Manager retrieves the value of Agent.
  • Set: Manager sets a value to the Agent.
  • Trap (Notification): Agent delivers information to Manager in asynchronous manner.
  • MIB (Management Information Base): Defines information to be sent and received through SNMP


SNMP Packet

SNMP sends and receives data through UDP. Due to the nature of UDP, the reliability of transmission is not guaranteed, but there is a simple aspect because it does not manage sessions.

 

161 and 162 are used as default ports. 161 is used for Get/Set and 162 is used for trap transmission.


SNMP Packet

IP headerUDP headerversioncommunityPDU-Typerequest-idError-statuserror-indexvariable bindings



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