diff --git a/xtr.pl b/xtr.pl
index 73a5131..344e667 100644
--- a/xtr.pl
+++ b/xtr.pl
@@ -12,24 +12,66 @@ use File::Fetch;
 use PerlIO::gzip;
 use LWP::UserAgent;
 use HTTP::Request;
+use Data::Validate::IP qw(is_ipv4);
 use Data::Dumper;
 
-### README
-# to install needed modules on debian:
-# * apt-get install libnet-whois-ip-perl libperlio-gzip-perl libdancer2-perl libnet-dns-perl libnet-traceroute-perl libdbi-perl libdbd-sqlite3-perl
 
-### vars
-my $dbfile = "ip2asn.db";
+
+###  README  #########################################################################################################################################
+# This is the client for the XTR (XiCoN Trace Route). It opens a port and listening to HTTP requests. It answers with a traceroute
+# in a json hash. The hash contains for each hop the IP, the PTR, the request time and the AS (Autonomous System).
+#
+# This client also tries to connect to a "master server" which helps keeping track of all the traceroute clients and their availability.
+#
+# This software uses the iptoasn database (https://iptoasn.com/) to determine the AS for each hop. To keep track of all ip to asn relations,
+# this software creates a local database file "ip2asn.db", which is a simple SQLite3 database with an index for faster searches.
+#
+# For now, the traceroutes are only IPv4. This will change in the future.
+######################################################################################################################################################
+
+
+###  INSTALL  ########################################################################################################################################
+# This is a standalone software which usually runs in the "foreground". Starting it in a screen session or via init.d/systemd/rc.d is
+# highly recommended. For testing, starting this script in a screen session is also fine.
+#
+# Either install all listed modules with "cpan -i <module>" or use your system's package manager (apt, yum, yast).
+# 
+# On Debian just install there packages:
+#  libnet-whois-ip-perl
+#  libperlio-gzip-perl
+#  libdancer2-perl
+#  libnet-dns-perl
+#  libnet-traceroute-perl
+#  libdbi-perl
+#  libdbd-sqlite3-perl
+#  libdata-validate-ip-perl
+#
+######################################################################################################################################################
+
+
+###  VARS  ###########################################################################################################################################
+my $VERSION = "0.4";
+my $dbfile = 'ip2asn.db';
 my $ip2asn_csv_url = 'http://iptoasn.com/data/ip2asn-v4-u32.tsv.gz';
-my $master_server = "xtr-master.xicon.eu";
-my $my_ip = get_my_ipv4();
+my $master_server = 'xtr-master.xicon.eu';
+my $get_my_ip_service = 'http://ipv4.xicon.eu/'; # some service, which returns just the ip of the requesting host (in this case, us.)
+my $client_protocol_version = 3;
+my $my_ip = get_my_ipv4($get_my_ip_service);
 my $my_ext_ip = ""; # set different ip, if access differs from default public ip
-my $my_port = 3000;
+my $my_port = 12111;
 my $my_ext_port = 0; # set different port, if public access port differs from app port
+######################################################################################################################################################
+
+
+######################################################################################################################################################
+###  NOTHING TO CHANGE BELOW HERE  ###################################################################################################################
+######################################################################################################################################################
+
 
 ### set vars
 set port => $my_port;
 if($my_ext_ip eq "") { $my_ext_ip = $my_ip; }
+if($my_ext_ip eq "0.0.0.0") { die "Couldn't determine my own IP"; }
 if($my_ext_port eq 0 || $my_ext_port eq "") { $my_ext_port = $my_port; }
 
 ### connect to database
@@ -45,12 +87,18 @@ hook 'before' => sub {
 };
 
 ### main get route
-get '/:ip' => sub {
+get '/v3/client/request/:ip' => sub {
 	my $ip = route_parameters->get('ip') || 8.8.8.8;
+	if(!is_ipv4($ip)) { status('bad_request'); return "invalid IP address" }
 	my $trace = traceit($dbh,$ip);
 	return encode_json $trace;
 };
 
+### return client protocol verison
+get '/v3/client/info/version' => sub {
+	return $client_protocol_version;
+};
+
 ### give the master server the info, that we are available
 if(send_server_status($master_server,$my_ext_ip,$my_ext_port,"1"))
 {
@@ -64,17 +112,19 @@ else
 ### catch "INT" signal to send the status to the master server
 $SIG{'INT'} = sub { send_server_status($master_server,$my_ext_ip,$my_ext_port,"0"); exit; };
 
-### start the loop
+### start the main loop
 start;
 
 ### if you reach this, you're done
 exit;
 
+
+
 sub send_server_status
 {
 	my ($master_server,$hostname,$port,$status) = @_;
-	my $url = "http://".$master_server."/v2/server/".$hostname."/".$port."/".$status;
-	my $ua = LWP::UserAgent->new(timeout => 10);
+	my $url = "http://".$master_server."/v3/server/add/".$hostname."/".$port."/".$status;
+	my $ua = LWP::UserAgent->new(timeout => 2);
 	my $req = HTTP::Request->new("PUT", $url);
 	my $response = $ua->request($req);
 	return $response->is_success;
@@ -82,9 +132,18 @@ sub send_server_status
 
 sub get_my_ipv4
 {
+	my ($ip_service) = @_;
 	my $ua = LWP::UserAgent->new(timeout => 10);
-	my $response = $ua->get("http://ipv4.xicon.eu/");
-	return $response->decoded_content;
+	my $response = $ua->get($ip_service);
+	if(is_ipv4($response->decoded_content))
+	{
+		return $response->decoded_content;
+	}
+	else
+	{
+		# no valid ip returned from ip service
+		return "0.0.0.0";
+	}
 }
 
 sub traceit
@@ -200,15 +259,18 @@ sub create_db_table
 	my $check_table_cmd = "SELECT name FROM sqlite_master WHERE type='table' AND name='ip2asn';";
 	my $check_table_sth = $dbh->prepare($check_table_cmd);
 	$check_table_sth->execute();
+
 	if(!$check_table_sth->fetch)
 	{
-		print "creating table...\n";
+		print "creating main table...\n";
 		my $create_table_cmd = "CREATE TABLE ip2asn( ip_from INTEGER, ip_to INTEGER, ip_as INTEGER)";
 		my $create_table_sth = $dbh->prepare($create_table_cmd);
 		$create_table_sth->execute();
-		#my $create_index_cmd = "CREATE INDEX ip2asnIndex ON ip2asn(ip_from,ip_to);";
-		#my $create_index_sth = $dbh->prepare($create_index_cmd);
-		#$create_index_sth->execute();
+
+		print "creating index table...\n";
+		my $create_index_cmd = "CREATE INDEX ip2asnIndex ON ip2asn(ip_from,ip_to);";
+		my $create_index_sth = $dbh->prepare($create_index_cmd);
+		$create_index_sth->execute();
 		return 1;
 	}
 	else