JFlow is a IP traffic flow sampler technology used by Juniper manufactured routers and switches. JFlow is considered a flow sampler technology much like Sflow, and when enabled on an interface; it allows packets in the input stream to be sampled. As the packets flow through an input stream the router/switch will look at each one, but only records new packets and discards any packets it has already seen.
JFlow is just one of three flow technologies available; among the 3 include Cisco’s Netflow and HP’s Sflow technologies. Each having their own strengths; Netflow records all packets while SFlow will only sample incoming traffic based on the packet ratio defined in the router configuration.