tcpdump usage
Synopsis tcpdump [ -AbdDefhHIJKlLnNOpqStuUvxX# ] [ -B buffer_size ] [ -c count ] [ -C file_size ] [ -E spi@ipaddr algo:secret,... ] [ -F file ] [ -G rotate_seconds ] [ -i interface ] [ --immediate-mode ] [ -j tstamp_type ] [ -m module ] [ -M secret ] [ --number ] [ --print ] [ -Q in|out|inout ] [ -r file ] [ -s snaplen ] [ -T type ] [...