Overview

Using a Juniper Networks M-series router, a selection of Physical Interface Cards (PICs)—including the Monitoring Services PIC, Monitoring Services II PIC, or Adaptive Services PIC—and other networking hardware, you can monitor traffic flow and export the monitored traffic. Monitoring traffic allows you to do the following:

• Gather and export detailed information about IPv4 traffic flows between source and destination nodes in your network.
• Sample all incoming IPv4 traffic on the monitoring interface and present the data in cflowd record format.
• Encrypt or tunnel outgoing cflowd records, intercepted IPv4 traffic, or both.
• Direct filtered traffic to different packet analyzers and present the data in its original format.
• Intercept unwanted traffic, discard it, and perform accounting on the discarded packets.

Passive Flow Monitoring

The M40e or M160 router used for passive flow monitoring does not route packets from monitored interfaces, nor does it run any routing protocols related to those interfaces; it only passes along intercepted traffic and receives traffic flows. Figure 7 shows a typical topology for the passive flow monitoring application.

Figure 7: Passive Flow Monitoring Application Topology

Traffic travels normally between Router 1 and Router 2. To redirect IPv4 traffic, you insert an optical splitter on the interface between these two routers. The optical splitter copies and redirects the traffic to the monitoring station, which is an M40e or M160 router. The optical cable connects only the receive port on the monitoring station, never the transmit port. This configuration allows the monitoring station to receive traffic only from the router being monitored but never to transmit it back.

If you are monitoring traffic flow, the Internet Processor II ASIC in the router forwards a copy of the traffic to the Monitoring Services PIC in the monitoring station. If there is more than one Monitoring Services PIC installed, the monitoring station distributes the load of the incoming traffic across the multiple PICs. The Monitoring Services PICs generate flow records in cflowd version 5 format, and the records are then exported to the cflowd collector.

If you are performing lawful interception of packets transiting between the two routers, the Internet Processor II ASIC filters the incoming traffic and forwards it to the Tunnel Services PIC. Filter-based forwarding is then applied to direct the traffic to the packet analyzers. Optionally, the intercepted traffic or the cflowd records can be encrypted by the ES PIC and then sent to their destination. Also, cflowd records can be processed by a flow collector.

With MPLS passive monitoring, the router can process MPLS packets with label values that do not have corresponding entries in the mpls.0 routing table. You can divert these unrecognized MPLS packets, remove the MPLS labels, and redirect the underlying IPv4 packets. This is equivalent to a default route for MPLS packets or a promiscuous label. Because this application does not use a Monitoring Services PIC, see the JUNOS Internet Software MPLS Applications Configuration Guide for more information about MPLS passive monitoring.

Active Flow Monitoring

For active flow monitoring, the monitoring station participates in the network as an active router. The major actions the router can perform during active flow monitoring are as follows:

• Sampling—The router selects and analyzes only a portion of the traffic.
• Port mirroring—The router copies entire packets and sends the copies to another interface.
• Multiple port mirroring—The router sends multiple copies of monitored packets to multiple export interfaces with the next-hop-group statement at the [edit forwarding-options] hierarchy level.
• Discard accounting—The router accounts for selected traffic before discarding it. Such traffic is not forwarded out of the router. Instead, the traffic is quarantined and deleted.