A Review on Simple Network Management Protocol (SNMP)

An Introduction

Background The Simple Network Management Protocol (SNMP) is an application-layer protocol that facilitates the exchange of management information between network devices. It is part of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite. SNMP enables network administrators to manage network performance, find and solve network problems, and plan for network growth. Two versions of SNMP exist: SNMP Version 1 (SNMPv1) and SNMP Version 2 (SNMPv2). Both versions have a number of features in common, but SNMPv2 offers enhancements, such as additional protocol operations. Standardization of yet another version of SNMP—SNMP Version 3 (SNMPv3)—is pending. This chapter provides descr iptions of the SNMPv1 and SNMPv2 protocol operations. Figure 52-1 illustrates a basic network managed by SNMP

Figure 1 SNMP facilitates the exchange of network information between devices.

SNMP application-layer protocol used to manage and monitor network devices and their functions. SNMP provides a common language for network devices to relay management information within single- and multivendor environments in a local area network (LAN) or wide area network (WAN). The most recent iteration of SNMP, version 3, includes security enhancements that authenticate and encrypt SNMP messages as well as protect packets during transit.

One of the most widely used protocols, SNMP is supported on an extensive range of hardware -- from conventional network equipment like routers, switches and wireless access points to endpoints like printers, scanners and internet of things (IoT) devices. In addition to hardware, SNMP can be used to monitor services such as Dynamic Host Configuration Protocol (DHCP). Software agents on these devices and services communicate with a network management system (NMS), also referred to as an SNMP manager, via SNMP to relay status information and configuration changes.

While SNMP can be used in a network of any size, its greatest value is evident in large networks. Manually and individually logging into hundreds or thousands of nodes would be extremely time-consuming and resource-intensive. In comparison, using SNMP with an NMS enables a network administrator to manage and monitor all of those nodes from a single interface, which can typically support batch commands and automatic alerts. SNMP is described in the Internet Engineering Task Force (IETF) Request for Comment (RFC) 1157 and in a number of other related RFCs.

Components of SNMP

There are four main components in an SNMP-managed network:

1. SNMP agent:This program runs on the hardware or service being monitored, collecting data about various metrics like bandwidth use or disk space. When queried by the SNMP manager, the agent sends this information back to the management system. An agent may also proactively notify the NMS if an error occurs. Most devices come with an SNMP agent preinstalled; it typically just needs to be turned on and configured.


2. SNMP-managed devices and resources: These are the nodes on which an agent runs.


3. SNMP manager (aka NMS):This software platform functions as a centralized console to which agents feed information. It will actively request agents send updates via SNMP at regular intervals. What a network manager can do with that information depends heavily on how feature-rich the NMS is. There are several free SNMP managers available, but they are typically limited in their capabilities or the number of nodes they can support. At the other end of the spectrum, enterprise-grade platforms offer advanced features for more complex networks, with some products supporting up to tens of thousands of nodes.


4. Management information base (MIB): This database is a text file (.mib) that itemizes and describes all objects used by a particular device that can be queried or controlled using SNMP. This database must be loaded into the NMS so that it can identify and monitor the status of these properties. Each MIB item is assigned an object identifier (OID).

How SNMP works

SNMP performs a multitude of functions, relying on a blend of push and pull communications between network devices and the management system. It can issue read or write commands, such as resetting a password or changing a configuration setting. It can report back how much bandwidth, CPU and memory are in use, with some SNMP managers automatically sending the administrator an email or text message alert if a predefined threshold is exceeded.

In most cases, SNMP functions in a synchronous model, with communication initiated by the SNMP manager and the agent sending a response. These commands and messages, typically transported over User Datagram Protocol (UDP) or Transmission Control Protocol/Internet Protocol (TCP/IP), are known as protocol data units (PDUs):

Conclusion

In general ensure that all the feature and network services are running and verify that the community string or SNMP user is properly configured on the Cisco Unified CM system. You configure the SNMP community string or user by choosing SNMP > V1/V2 > Community String or SNMP > V3> User in Cisco Unified Serviceability.