What is the purpose of a packet sniffer?
The network card on your computer is inundated with network traffic. Some of this traffic is addressed to your machine, or a multicast address that your machine is listening for, and some of it isn’t addressed to your machine at all. Normally the “garbage” traffic that isn’t addressed to your machine is simply ignored by the network card, and the stuff that is for your machine is parsed through the OSI model and delivered to the apps they’re designed to talk to. When you use a packet sniffer, it puts your network card in “promiscuous mode” and the card passes a copy of all network traffic it receives to the packet sniffer app before dumping it as garbage, or delivering it to the destination app on your machine. You can see (sometimes on a bit-for-bit level) what’s going on on your network. This can be useful for troubleshooting, preventative maintenance, or for malicious purposes like password interception or session hijacking.
