#!/usr/bin/perl# tests to see if a host is up# by sending tcp packets (syn)# to all ports.# even if all ports are closed,# the host will probably send an# rst back, which pdump will catch.use pdump::Sniff;die "usage: $0 <host>\n" unless @ARGV == 1;$| = 1;$tout = 10;$host = $ARGV[0];$dev = pdump::Sniff::lookupdev($tout);$ip = ${ifaddrlist()}{$dev};$packet_tcp = new pdump::Sniff({tcp=>{}});$filt_tcp = "ip proto \\tcp and src host $host and dst host $ip";$pcap_tcp = $packet_tcp->pcapinit($dev, $filt_tcp, 1500, 60, 0);$offset_tcp = linkoffset($pcap_tcp);if ($fork1 = fork) { &send;}if ($fork2 = fork) { loop $pcap_tcp, -1, \&check_tcp, \@packet_tcp;}sub check_tcp{ print "TCP reply from $host recieved, host is up\n"; kill(9, $fork1); die "\n";}sub send { sleep 3; foreach (1 .. 65535) {  $a = new pdump::Sniff;  $a->set({   ip => {        saddr => $ip,        daddr => $host,        },   tcp => {        dest => $_,        source => 1337,        seq => 31337,        syn => 1,        },  });  $a->send; } die "No TCP reply...host seems to not be up\n";}