How SNMP works?

The SNMP architecture consists of three key components, managed devices, agents and network management systems (NMS).

Managed Devices: These devices are network nodes that contain SNMP agents. These devices collect and store management information in the Management Information Base (MIB) and allow access to these MIBs to the NMSs through SNMP.Examples of managed devices include routers, switches, servers, computer stations and network printers.

Agents: These are management software modules that reside on a manged device. They collect and store the state of the managed device and translate this information into a form compatible with SNMP.

Network Management Systems: These are applications that monitor and control managed devices. They provide the processing power and resources required for network management.

The above figure displays the relationship between managed devices, agents and network management devices.

The SNMP exchanges network management information through messages known as Protocol Data Units (PDUs). These PDUs are sent to nodes on a network, they contain variables that have both attributes and values.

The varibles contain the following attributes:

  • the variable title
  • the data type of the variable (eg. integer, string)
  • whether the variable is read-only or read-write
  • the value of the variable

There are five types of messages (PDUs) that SNMP employs to monitor a network device. Two deal with reading terminal, two deal with setting terminal data and a trap. The trap is used to monitor network events such as terminal start-up and shut-down.

The network management system can request attributes form the the agent and it can set attribute values with in the agent.

Standard SNMP messages

Format for polling:
Format for trap:

Advantages of SNMP

The most important advantage of SNMP that made it popular is its simple design and implementation. The simple design allows users to easily program varibles that they want to monitor. Expandibility of the SNMP is also another advantage, because of its simple design, the protocol can be updated to meet future needs.

Another advantage of SNMP is that it is widley implemented. Almost all major vendors of internetwork hardware, such as bridges and routers, design their products to support SNMP, making it very easy to implement.

Disadvantages of SNMP

SNMP has security gaps that can give network intruders access to the information carried along the network. Intruders could also potentially shut down some terminals. However the SNMP verion 2 has fixed some security issues regarding privacy of data, authentication and access control.

Another disadvantage of SNMP is that its simple design means that the information it deals with is neither detailed nor well-organized enough to deal with the expanding modern networking requirements.