#!/usr/bin/perl
# luna@aditel.org
#
use IO::Socket::INET;
use Net::DHCP::Packet;
use Net::DHCP::Constants;
use IO::Select;


###CONFIG HERE
my($iface)="eth0";
my($timeout)="10"; #Timeout in seconds
#####################

#Some dhcp servers needs mac address in the msg to match with layer 2 information...
#Getting our own mac address... (ioctl way is so platform dependent... :P)
$iface=quotemeta($iface);
$mymac=`/sbin/ifconfig $iface |grep HW`;
chomp($mymac);
$mymac=~ s/.*(.{2}):(.{2}):(.{2}):(.{2}):(.{2}):(.{2}).*/$1$2$3$4$5$6/g;

# creat DHCP Packet
$discover = Net::DHCP::Packet->new(
               xid => int(rand(0xFFFFFFFF)), # random xid
               Flags => 0x8000,              # ask for broadcast
               Chaddr=>$mymac,
               DHO_DHCP_MESSAGE_TYPE() => DHCPDISCOVER()
           );

#Sender socket
$handle = IO::Socket::INET->new(Proto => 'udp',
                                  Broadcast => 1,
                                  PeerPort => '67',
                                  LocalPort => '68',
                                  PeerAddr => '255.255.255.255',
				  ReuseAddr=>1)
                       or die "socket: $@";     # yes, it uses $@ here

#Receiver socket (should bind to ANY addres,(response may come as broadcast))
$bsock = IO::Socket::INET->new(LocalPort => 68, 
                               Proto => "udp", 
                               Broadcast => 1,
                               ReuseAddr=>1)
                 or die "socket: $@";

$control=new IO::Select($bsock);

#Send dhcp discover
$handle->send($discover->serialize())
                       or die "Error sending broadcast inform:$!\n";

#Receive responses
my(%servers);
while ($control->can_read($timeout)) {
    $bsock->recv($newmsg, 1024);
    $packet = Net::DHCP::Packet->new($newmsg);
#    print STDERR $packet->toString();
    my($ip1,
       $ip2,
       $ip3,
       $ip4)=unpack("CCCC",$packet->getOptionRaw(DHO_DHCP_SERVER_IDENTIFIER()));
    $servers{"$ip1.$ip2.$ip3.$ip4"}=1;
}
print "Active DHCP server(s) on the network: ".join(",",keys(%servers))."\n";