Dell PowerConnect 7048P User Manual - Page 393

sFlow Sampling The sFlow Agent in the PowerConnect 7000 Series switch software uses two forms of sampling: • Statistical packet-based sampling of switched or routed Packet Flows • Time-based sampling of counters Packet Flow Sampling and Counter Sampling are performed by sFlow Instances associated with individual Data Sources within an sFlow Agent. Both types of samples are combined in sFlow datagrams. Packet Flow Sampling creates a steady, but random, stream of sFlow datagrams that are sent to the sFlow Collector. Counter samples may be taken opportunistically to fill these datagrams. To perform Packet Flow Sampling, an sFlow Sampler Instance is configured with a Sampling Rate. Packet Flow sampling results in the generation of Packet Flow Records. To perform Counter Sampling, an sFlow Poller Instance is configured with a Polling Interval. Counter Sampling results in the generation of Counter Records. sFlow Agents collect Counter Records and Packet Flow Records and send them as sFlow datagrams to sFlow Collectors. Packet Flow Sampling Packet Flow Sampling, carried out by each sFlow instance, ensures that any packet observed at a Data Source has an equal chance of being sampled, irrespective of the Packet Flow(s) to which it belongs. Packet Flow Sampling is accomplished as follows: • A packet arrives on an interface. • The Network Device makes a filtering decision to determine whether the packet should be dropped. • If the packet is not filtered (dropped) a destination interface is assigned by the switching/routing function. • A decision is made on whether or not to sample the packet. The mechanism involves a counter that is decremented with each packet. When the counter reaches zero a sample is taken. Monitoring Switch Traffic 393