You really don't want to code this yourself. Here is a trivial example for interest sake only. It shows you how to build a packet (and its checksum) and that you do get data back which as you can see it is encoded in a binary packet format. 

use IO::Socket;

use constant ICMP_ECHO      => 8;
use constant SUBCODE        => 0; # No ICMP subcode for ECHO and ECHOR
+EPLY
use constant ICMP_STRUCT    => "C2 n3 A64";

my $icmp = IO::Socket::INET->new(   PeerAddr => 'perlmonks.org',
                                    Proto=>'icmp'
);
print "Got socket\n";

my $data = '1'x64;
my $seq = 1;
my $checksum = 0; 
my $msg = pack(ICMP_STRUCT, ICMP_ECHO, SUBCODE, $checksum, $$, $seq, $
+data);
$checksum = checksum($msg);
my $msg = pack(ICMP_STRUCT, ICMP_ECHO, SUBCODE, $checksum, $$, $seq, $
+data);

print "Sending: $msg\n";
$icmp->send($msg);
$icmp->recv(my $buf, 1500);
print "Got: $buf";
print "Done\n";

sub checksum {
  my ($msg ) = @_;
  my $len_msg = length($msg);
  my $num_short = int($len_msg / 2);
  my $chk = 0;
  for my $short (unpack("n$num_short", $msg)) {
    $chk += $short;
  } 
  $chk += (unpack("C", substr($msg, $len_msg - 1, 1)) << 8) if $len_ms
+g % 2;
  $chk = ($chk >> 16) + ($chk & 0xffff);
  return(~(($chk >> 16) + $chk) & 0xffff);
}

[download]

cheers

tachyon

In reply to Re^3: udp recv question by tachyon
in thread udp recv question by smackdab

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