Rapid growth in IP networks have created a need for increased network bandwidth and better network manageability. Network operators require network-wide visibility to provide the best class of service for their users. J-Flow, a flow monitoring service on Juniper Networks devices, is a tool specifically designed to meet this need, providing network operators with access to IP flow information and improved visibility across their networks. With J-Flow, network devices such as routers, firewalls, and switches collect flow data and export that information to flow collectors. The collected data provides critical information about traffic in the network and aids in tasks such as billing, traffic engineering, capacity planning, and traffic analysis for peering policy decisions.

A flow is a sequence of packets with common characteristics such as same source and destination IP address, transport layer port information, and type of IP protocol. Network devices differentiate flows depending upon their architecture, implementation, and device configuration. Each of these devices collects flow information on traffic that is received or sent through it. This information can then be logged locally or sent to an external information collector that will provide fine-grained information on network visibility for a variety of purposes, such as enterprise accounting and departmental chargeback, Internet service provider (ISP) billing, data monitoring and profiling, security analysis, and data mining for marketing purposes.