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Processing SNMP GET Requests for MDI Metrics on MX Series Routers

A query on-demand mechanism without caching facility is used to process the SNMP Get requests. The Routing Engine queries the Packet Forwarding Engine to obtain the computed metrics on every Get request. The Routing Engine does not maintain computed metrics locally. No additional memory is required to cache queried metrics. The network management system (NMS) server can receive latest information on every Get request, especially regarding the MDI records because MDI records are updated very frequently. However, querying the Packet Forwarding Engine PFE on each GET request is resource-consuming if the volume of metrics is large. The response to a Get request might be relatively delayed as the Routing Engine has to poll the Packet Forwarding Engine to obtain the metrics.

Inline MDI metrics are real-time data where cached information might not be valid. Reporting cached or invalid metrics is not beneficial because it a real-time monitoring feature. An increase in the number of flows and number of MDI records per flow causes a proportional increase in the volume of memory required in the Routing Engine to store flows and MDI records for all flows. Because asynchronous traps are generated for threshold with enough contents, frequent Get request from NMS are not highly expected, reducing the periodicity of polling to the Packet Forwarding Engine. SNMP traps are triggered with the severity level of Info, Warning, Critical, or Cleared. A trap with the cleared severity level is used to clear an alarm.

Whenever a change in the alarm level occurs, the designated trap is triggered. For example, if the delay factor (DF) alarm changes from informational level to warning level, or from warning to critical, the mdiDFAlarm trap is triggered. Alarm can be immediate or average. If the immediate alarm is configured, an immediate trap is raised at the end of interval duration if the metric value exceeds the configured range. If the average alarm is configured, a trap is generated, based on the average value for specified number of interval duration.

Storm control is applied for SNMP traps at the flow level and not at the FPC level. The NMS system can obtain SNMP trap from all the flows even if multiple flows are generating traps at approximately the same time. If multiple flows are generating traps at nearly the same time, NMS is flooded by many traps at the same time. For example, no traffic received on a logical interface owing to any reason can trigger all alarms and cause an avalance of alarms on the NMS server.