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Use tcpdump to listen to network interface traffic.
tcpdump is a useful utility to print out descriptions of contents of packets flowing through network interface card which match a given boolean expression.
sudo tcpdump -i wlan -v 'tcp port 80'
The -i specifies the interface to listen on. The -v option specifies verbosity of packet information such as time to live, identification, total length and options in ip packet. The expression specifies a pcap-filter used to decide which packets to print. Here we listen for tcp traffic with either source or destination port set to 80.
See man pcap-filter for details on filters.
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