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[M/MX/T] Counter mismatch between router interface and flow server

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Article ID: KB25000 KB Last Updated: 21 Mar 2014Version: 1.0
Summary:

The statistics on the ingress interface and on the interface of the flow server do not match. This article explains why this is expected behavior.

Symptoms:
The statistics on the ingress interface and on the interface of the flow server cannot be matched.

Cause:

This is an expected behavior.

The statistics on ingress interface cannot be matched with the statistics on the flow server because all the packets samples are not sent to flow server. At a configurable regular interval, a digest packet which may contain the information of hundreds of flows sampled.

Solution:

This is an expected behavior. The statistics on ingress interface cannot be matched with the statistics on the flow server because all the packets samples are not sent to flow server. At a configurable regular interval, a digest packet which may contain the information of hundreds of flows sampled.

As per sampling functionality, a digest packet is sent to flow server which may have the information about hundreds of flows sampled at a regular interval.

Traffic sampling is not meant to capture all packets received by a router. Juniper Networks does not recommend excessive sampling (a rate greater than 1/1000 packets), because it can increase the load on processor and competes with other routing engine tasks. Be careful when choosing  the number of samples per second.

There is a hard limit of 7000 on the routing engine. A user will never get more than that with RE-based sampling. To be able to sample more pps, AS-PIC or PM-PIC (monitoring PIC) is required.

For more information, please refer to the following links:

Configuring Traffic Sampling

Traffic Sampling, Forwarding and Monitoring Overview
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