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Defining SNMP (Simple Network Management Protocol): Glossary

Understanding everything that makes up SNMP can be a large task for someone who is new to the protocol. Here we'll define SNMP terms that are common in the managed network monitoring and control industry.


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Agent: An SNMP entity - hardware device or software program - that reports to an SNMP master station (also called managers). In network alarm management, an SNMP agent is typically an RTU, but other network devices like switches, routers and hubs can also act as SNMP agents. An SNMP agent community can also be a subsection of a larger device, like the SNMP Agent software module in T/Mon LNX, which mediates T/Mon alarms to SNMP traps.

SNMP Community string: An SNMP security password. There are three kinds of common SNMP strings:

Compiling: The process of importing a MIB file into an SNMP manager. To compile properly, a MIB file must be formatted in a text file according to the Structure of Management Information (SMI) standard.

COS (Change of State) alarm: A telemetry alarm that is clearly labeled as reporting a change in status from clear to alarm or from alarm to clear.

Event: In SNMP terms, any change of status in a managed object in the network. SNMP equipment can generate traps for many different kinds of events, not all of which are important for telemetry. The ability to filter unimportant events is essential for high-quality SNMP alarm management

SNMP Get: An SNMP message issued by a manager that requests the status of managed devices.

SNMP Get Next: An SNMP message issued by a manager, used to walk down a range of OIDs. The GetNext request retrieves the value of the managed object one number after the OID listed in the request.

SNMP Get Response: SNMP message issued by an agent in response to a Get, GetNext or Set requests from your network SNMP manager.

Internet Protocol (IP): the network layer datagram protocol of the TCP/IP protocol suite. SNMP runs over UDP, which in turn runs over IP.

Managed Objects: Managed object in network management are the devices that can be read or overwritten by the SNMP manager, like alarm status, control relay status, system uptime, etc. In SNMP terms, every network device is defined in the MIB as a set of managed objects.

Management Information Base (MIB): The MIB is a data structure that describes SNMP network elements as a list of data objects. To monitor network SNMP devices, your SNMP manager must compile the MIB file for each equipment type in your network.

Manager: A top-level SNMP master system (hardware or software) serving as the human interface to the SNMP network. The manager can issue a large volume of requests for Get, GetNext and Set requests to agents while receiving a large volume of GetResponse and Trap messages.

NMS: Network Management Software or Network Management System. Another term for SNMP manager software or hardware.

Object Identifier (OID): A number that uniquely identifies a managed object in an SNMP network. An OID consists of a series of numbers separated by decimal points. Each decimal point represents a leaf node in the tree structure of the MIB.

For example, all common SNMP OIDs for DPS Telecom equipment begin with the numbers 1.3.6.1.4.1.2682. This sequence represents: iso (1); org (3); dod (6); internet (1); private (4); enterprises (1); dpsInc (2682).

Protocol Data Unit (PDU): An SNMP message. There are 5 types of PDU in SNMP v1: Get, GetNext, Set, GetResponse and Trap.
Packet Internet Gopher (PING): An ICMP (Internet Control Message Protocol) echo request to determine whether a device on an IP network is online.

Proxy agent: A network connection SNMP agent that translates non-SNMP messages and inputs to SNMP. In network alarm monitoring, a proxy agent is usually an RTU that converts contact closure inputs to SNMP traps, like the NetGuardian 832A. Devices that mediate other alarms in other protocols to SNMP, like the NetMediator T2S (TBOS to SNMP) is also a proxy agent.

Set: An SNMP message issued by a manager instructing an agent to change a Managed object to a new value
Structure of Management Information (SMI): the standard that defines the MIB structure.

Simple Network Management Protocol (SNMP): The SNMP meaning is that it is the standard TCP/IP protocol for managing IP network devices. The most common version of SNMP is the SNMPv3.

Standing alarm list: A list of all uncleared alarms, as maintained by a full-featured network alarm management system. Standard SNMP managers automatically delete all acknowledged traps, but a standing alarm list displays every alarm that has not been reported as cleared by the monitoring equipment the network administrators.

Transmission Control Protocol (TCP): the more common transport layer protocol in the TCP/IP suite. TCP is considered a "reliable" protocol because it establishes a connection between the host and the recipient, guaranteeing delivery. UDP, the transport protocol used for SNMP does not establish a connection or guarantee delivery.

Trap: An SNMP message issued by an SNMP agent that reports an event.

User Datagram Protocol (UDP): the transport layer protocol used to send SNMP messages. Unlike TCP, UDP is a connectionless protocol that does not guarantee delivery of the data packet. However, UDP uses fewer network resources than TCP, making it more suitable for transporting a large number of status messages.

Variable Binding: the data field of a GetResponse or Trap PDU. Each variable binding lists a managed object and its current value.


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