How packet sniffer work?please describe briefly?

Answer 1

Example uses
A packet sniffer for a token ring network could detect that the token has been lost or the presence of too many tokens (verifying the protocol).
A packet sniffer could detect that messages are being sent to a network adapter; if the network adapter did not report receiving the messages then this would localize the failure to the adapter.
A packet sniffer could detect excessive messages being sent by a port, detecting an error in the implementation.
A packet sniffer could collect statistics on the amount of traffic (number of messages) from a process detecting the need for more bandwidth or a better method.
A packet sniffer could be used to extract messages and reassemble into a compete form the traffic from a process, allowing it to be reverse engineered.
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Answer 2

A packet analyzer (additionally standard as a community analyzer, protocol analyzer or sniffer, or for particular kinds of networks, an Ethernet sniffer or instant sniffer) is computing gadget utility or computing gadget hardware that could intercept and log site visitors passing over a digital community or area of a community.[a million] As records streams flow around the community, the sniffer captures each packet and at last decodes and analyzes its content fabric in accordance to the right RFC or different specs.

Answer 3

http://www.grc.com/oo/packetsniff.htm