Configuring J-Flow Statistics; Overview; Interface Sampling - Juniper IP SERVICES - CONFIGURATION GUIDE V 11.1.X Configuration Manual

Chapter 3

Configuring J-Flow Statistics

Overview

Interface Sampling

This chapter describes how to configure J-Flow statistics on your ERX router; it
contains the following sections:
Overview on page 95
Platform Considerations on page 98
Before You Configure J-Flow Statistics on page 98
Configuring Flow-Based Statistics Collection on page 98
Monitoring J-Flow Statistics on page 106
The JUNOSe J-Flow feature provides a method by which you can collect IP traffic
flow statistics on your routing devices. J-Flow does not require any special protocol
for connection setup. It also does not require any external changes to networked
traffic, packets, or any other devices in the network. In other words, J-Flow is
transparent to the existing network, including end stations and application software
and network devices such as LAN switches.
The JUNOSe implementation of J-Flow allows you to export data to the UDP port of
a remote workstation for data collection and further processing. In addition, the
ability to enable J-Flow on an individual virtual router, interface, or subinterface
allows you to collect network statistics for specific locations within your network.
For any given IP interface, enabling J-Flow causes packets from the input stream to
be sampled at a globally configured rate. For each packet sampled, the main flow
cache is examined to see if there is an existing entry. If no entry exists, J-Flow creates
a new entry and records attributes of the flow. If the packet matches an existing
entry, J-Flow updates the existing flow.
In general, the system samples packets that it can forward. In other words, the system
does not sample packets that it discards. As sampling occurs, the system records
flow characteristics as they would appear for a packet that the virtual router transmits.
This means, for example, that if a packet uses the address of an output interface or
next-hop value altered by a policy setting, the system records the altered value in
the flow record.
95
Overview