SNMP (Simple Network Management Protocol) 

Simple Network Management Protocol (SNMP) is an application layer protocol that is used for network device management. This protocol can collects and manipulate valuable network information from switches, routers, servers, printers, and other network-attached devices.
An SNMP-managed network consists of two components:

• Network management station (NMS) – the software which runs on the administrative computer. This software gathers SNMP data by requiring the devices on the network to disclose certain information. Devices can also inform the NMS about problems they are experiencing by sending an SNMP alert (called a trap).
• Agent – the software which runs on managed devices and reports information via SNMP to the NMS.

Consider the following example:

The router R1 is configured to send SNMP traps to the NMS Station. If a problem occurs, the router will send an SNMP trap to Host A. For example, if there is a port security violation on R1, the router will send the SNMP trap, notifying that there has been a potential security breach on the network.
NOTE – SNMP agents use a UDP port 161, while the manager uses a UDP port 162. The current SNMP version is SNMPv3. The prior versions, SNMPv1 and SNMPv2 are considered obsolete and should not be used.