SNMP overview

Simple Network Management Protocol (SNMP) is a set of application layer protocols for managing complex networks. Devices within a network use SNMP to send messages, called protocol data units (PDUs), to different parts of a network.

Network management using SNMP requires three components:

SNMP manager—Typically, network management systems (NMS) that manage networks by monitoring the network parameters, and optionally, setting parameters in managed devices. The SNMP manager communicates to the devices within a network using the SNMP protocol.
SNMP agent—Software that resides in the managed devices in the network, and collects and stores data from these devices. Each device hosts an SNMP agent. The agent receive requests from the SNMP manager and responds with the requested data. In addition, the agent can asynchronously alert the SNMP manager about events by using special PDUs called traps.
Multiple instances of the same MIB module can support a single SNMP agent by mapping a specific key called a context name to a virtual routing and forwarding (VRF) instance created within the Extreme device.
Management Information Base (MIB)—Hierarchical database where SNMP agents in the managed devices store the data about these devices. The MIB is is structured on the standard specified in the RFC 2578 [Structure of Management Information Version 2 (SMIv2)].
An SNMP manager can issue read or write operations to retrieve and use the MIB objects to manage and monitor devices on the network. However, the MIB structure determines the scope of management access allowed by a device.

The SNMP server on the Extreme device supports SNMP version 1 (SNMPv1), SNMP version 2 (SNMPv2), and SNMP version 3 (SNMPv3).

SNMPv1 and SNMPv2 use community strings associated to SNMP groups. The group maps the user to MIB objects called SNMP views. The views restrict the access of the MIB OIDs .
SNMPv3 provides additional security through authenticated users associated with groups to restrict the access of MIBs for SNMP requests through SNMP views.

Also, the device supports the configuration of trap hosts as a trap recipient to receive filtered traps based on their severity level, and optionally receive SNMP communication through a VRF.

When clear command is issued to clear interface statistics, counters are cleared only from CLI version of the statistics and the SNMP version of the statistics are kept intact (SNMP stats preservation). SNMP accumulates the counters and displays aggregate values via IF-MIB queries. These MIB statistics can preserved by using the snmp-server preserve-statistics command by enabling or disabling these MIB statistics when the clear interface statistics command is issued.

snmp-server preserve-statistics command is enabled, SNMP MIB statistics are preserved .i.e clear command only clears counters from command line interface and not from SNMP IF-MIB. When snmp-server preserve-statistics is disabled, clear command deletes the counters from both the command line interface and SNMP versions.

Note

By default, preserving of MIB statistics is enabled. User has to execute the CLI command to disable preserving of MIB statistics.

device(config)#  snmp-server preserve-statistics disable
device(config)# no  snmp-server preserve-statistics disable