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PHP : Function Reference : Network Functions

Network Functions



No external libraries are needed to build this extension.


There is no installation needed to use these functions; they are part of the PHP core.

Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

Table198.Network Configuration Options

Name Default Changeable Changelog
define_syslog_variables "0" PHP_INI_ALL

For further details and definitions of the PHP_INI_* constants, see the AppendixI, php.ini directives.

Here's a short explanation of the configuration directives.

define_syslog_variables boolean

Whether or not to define the various syslog variables (e.g. $LOG_PID, $LOG_CRON, etc.). Turning it off is a good idea performance-wise. At runtime, you can define these variables by calling define_syslog_variables().

Resource Types

This extension defines a file pointer resource returned by fsockopen() and pfsockopen().

Predefined Constants

The constants below are always available as part of the PHP core.

Table199.openlog() Options

Constant Description
LOG_CONS if there is an error while sending data to the system logger, write directly to the system console
LOG_NDELAY open the connection to the logger immediately
LOG_ODELAY (default) delay opening the connection until the first message is logged
LOG_PERROR print log message also to standard error
LOG_PID include PID with each message

Table200.openlog() Facilities

Constant Description
LOG_AUTH security/authorization messages (use LOG_AUTHPRIV instead in systems where that constant is defined)
LOG_AUTHPRIV security/authorization messages (private)
LOG_CRON clock daemon (cron and at)
LOG_DAEMON other system daemons
LOG_KERN kernel messages
LOG_LOCAL0 ... LOG_LOCAL7 reserved for local use, these are not available in Windows
LOG_LPR line printer subsystem
LOG_MAIL mail subsystem
LOG_NEWS USENET news subsystem
LOG_SYSLOG messages generated internally by syslogd
LOG_USER generic user-level messages
LOG_UUCP UUCP subsystem

Table201.syslog() Priorities (in descending order)

Constant Description
LOG_EMERG system is unusable
LOG_ALERT action must be taken immediately
LOG_CRIT critical conditions
LOG_ERR error conditions
LOG_WARNING warning conditions
LOG_NOTICE normal, but significant, condition
LOG_INFO informational message
LOG_DEBUG debug-level message

Table202.dns_get_record() Options

Constant Description
DNS_A IPv4 Address Resource
DNS_MX Mail Exchanger Resource
DNS_CNAME Alias (Canonical Name) Resource
DNS_NS Authoritative Name Server Resource
DNS_PTR Pointer Resource
DNS_HINFO Host Info Resource (See IANA's Operating System Names for the meaning of these values)
DNS_SOA Start of Authority Resource
DNS_TXT Text Resource
DNS_ANY Any Resource Record. On most systems this returns all resource records, however it should not be counted upon for critical uses. Try DNS_ALL instead.
DNS_AAAA IPv6 Address Resource
DNS_ALL Iteratively query the name server for each available record type.

Table of Contents

checkdnsrr — Check DNS records corresponding to a given Internet host name or IP address
closelog — Close connection to system logger
debugger_off — Disable internal PHP debugger (PHP 3)
debugger_on — Enable internal PHP debugger (PHP 3)
define_syslog_variables — Initializes all syslog related constants
dns_check_record — Alias of checkdnsrr()
dns_get_mx — Alias of getmxrr()
dns_get_record — Fetch DNS Resource Records associated with a hostname
fsockopen — Open Internet or Unix domain socket connection
gethostbyaddr — Get the Internet host name corresponding to a given IP address
gethostbyname — Get the IP address corresponding to a given Internet host name
gethostbynamel — Get a list of IP addresses corresponding to a given Internet host name
getmxrr — Get MX records corresponding to a given Internet host name
getprotobyname — Get protocol number associated with protocol name
getprotobynumber — Get protocol name associated with protocol number
getservbyname — Get port number associated with an Internet service and protocol
getservbyport — Get Internet service which corresponds to port and protocol
header — Send a raw HTTP header
headers_list — Returns a list of response headers sent (or ready to send)
headers_sent — Checks if or where headers have been sent
inet_ntop — Converts a packed internet address to a human readable representation
inet_pton — Converts a human readable IP address to its packed in_addr representation
ip2long — Converts a string containing an (IPv4) Internet Protocol dotted address into a proper address
long2ip — Converts an (IPv4) Internet network address into a string in Internet standard dotted format
openlog — Open connection to system logger
pfsockopen — Open persistent Internet or Unix domain socket connection
setcookie — Send a cookie
setrawcookie — Send a cookie without urlencoding the cookie value
socket_get_status — Alias of stream_get_meta_data()
socket_set_blocking — Alias of stream_set_blocking()
socket_set_timeout — Alias of stream_set_timeout()
syslog — Generate a system log message

Code Examples / Notes »


When I was working on a project I ran into this problem with redirecting. My solution is as follows:
header("Refresh: 5; url=../main/main.php?".session_id()."");
This allowed me to pass the session_id() which is used throughout site to make sure user has loged in.
I hope this helps!


Ups. The function has a bug, though the example still works with it. Just replace the $_POST variables by the function parameters.
function isIPIn($ip, $net, $mask) {
  //doesn't check for the return value of ip2long
  $ip = ip2long($ip);
  $rede = ip2long($net);
  $mask = ip2long($mask);
  $res = $ip & $mask;
  return ($res == $rede);


To find if an IP is in a net/mask (very fast):
function isIPIn($ip,$net,$mask) {
  $binnet=str_pad( decbin($lnet),32,"0","STR_PAD_LEFT" );
  $binip=str_pad( decbin($lip),32,"0","STR_PAD_LEFT" );
This function can be compacted, avoiding some variable settings, but the function will not be too clear to read...
Example code, used to made a kind of location service network-based:
$n = array ( ""   => "TUSCANY",
            ""   => "- Florence",
            ""   => "- Pisa",
            ""   => "- Siena",
            "" => "- Tuscan Archipelago",
            "" => "--- Elba Island",
            "" => "--- Capraia Island",
            "" => "--- Giannutri Island");
// Normally you should use the following line
// This is first example: returns Tuscany/Pisa
$myip = "";
// This is second example: returns Tuscany/T.Arch./Elba
$myip = "";
echo "Your position:<br />\n";
foreach ( $n as $k=>$v ) {
  if (isIPIn($myip,$net,$mask)) {
      echo $n[$k]."<br />\n"; }
and so on...


Regarding samuele's note:
You can get faster code if you apply directly what happens in  network devices, such as routers. If you AND (logic operation) the remote ip against the local netmask the result will be the network ip if the remote ip is from the local network. Example: = 11000000.10101000.00000000.00010000
& = 11111111.11111111.11111111.00000000
-------------------------------------------------------------- = 11000000.10101000.00000000.00000000
And now the code. My example uses a html form where you place the values you want to test:
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST">
Hope you find this useful.
IP to check: <input type="text" name="ip">
Local network ip: <input type="text" name="net">
Local netmask: <input type="text" name="mask">
<input type="submit" name="check" value="Check it!">
* @param string $ip IP to check in dotted decimal format
* @param string $net Network IP in dotted decimal format
* @param string $mask Netmask in dotted decimal format
* @returns true if the ip belongs to the network, false otherwise
function isIPIn($ip, $net, $mask) {
//doesn't check for the return value of ip2long
$ip = ip2long($_POST['ip']);
$rede = ip2long($_POST['net']);
$mask = ip2long($_POST['mask']);

$res = $ip & $mask;

return ($res == $rede);
if (isset($_POST['check'])) {
echo isIPIn($_POST['ip'], $_POST['net'], $_POST['mask']) ? "IP IN.": "IP OUT.";


Previous example of IP range to CIDR list does not cope with ranges as well as the perl Net::Netmask range2cidrlist() function. In PHP this looks like
function imask($this)
// use base_convert not dechex because dechex is broken and returns 0x80000000 instead of 0xffffffff
return base_convert((pow(2,32) - pow(2, (32-$this)))), 10, 16);
function imaxblock($ibase, $tbit)
while ($tbit > 0)
$im = hexdec(imask($tbit-1));
$imand = $ibase & $im;
if ($imand != $ibase)
return $tbit;
function range2cidrlist($istart, $iend)
// this function returns an array of cidr lists that map the range given
$s = explode(".", $istart);
// PHP ip2long does not handle leading zeros on IP addresses! 172.016 comes back as 172.14, seems to be treated as octal!
$start = "";
$dot = "";
while (list($key,$val) = each($s))
$start = sprintf("%s%s%d",$start,$dot,$val);
$dot = ".";
$end = "";
$dot = "";
$e = explode(".",$iend);
while (list($key,$val) = each($e))
$end = sprintf("%s%s%d",$end,$dot,$val);
$dot = ".";
$start = ip2long($start);
$end = ip2long($end);
$result = array();
while ($end > $start)
$maxsize = imaxblock($start,32);
$x = log($end - $start + 1)/log(2);
$maxdiff = floor(32 - floor($x));
$ip = long2ip($start);
if ($maxsize < $maxdiff)
$maxsize = $maxdiff;
$start += pow(2, (32-$maxsize));
return $result;


Ported Net::Netmask perl module:

PHP miss CIDR functions.
This one will convert a CIDR like this: -> -
127.0/16 -> -
function cidrconv($net) {
$n=3-substr_count($net, ".");
if ($n>0) { for ($i=$n;$i>0;$i--) $start.=".0"; }
for ($i=0;$i<32;$i++) {
if ($bits1[$i]==$bits2[$i]) $final.=$bits1[$i];
if ($bits1[$i]==1 and $bits2[$i]==0) $final.=$bits1[$i];
if ($bits1[$i]==0 and $bits2[$i]==1) $final.=$bits2[$i];
return $start." - ".long2ip(bindec($final));


More socket functions can be seen here :


In Trevor Hemsley's translation of the perl range2cidr function, the
while ($end > $start)
condition should be
while ($end >= $start)
otherwise it won't work for /32s, ie if you feed range2cidr("", "").
-- nex


If you want to get the interface of an IP, based on the local route table, use this.
function GetIfaceforIP($user_ip)
   $route = "/bin/netstat -rn";
   exec($route, $aoutput);
   foreach($aoutput as $key => $line)
       if($key > 1)
           $line = ereg_replace("[[:space:]]+",",",$line);
           list($network, $gateway, $mask, $flags, $mss, $window, $irtt, $iface) = explode(",", $line)
           if((ip2long($user_ip) & ip2long($mask)) == ip2long($network))
               return $iface;

david gastaldin

Here a IP-Range to CIDRs function that I wrote for the purpose of filling my Postfix client.cidr with ripe-ncc data to block spamming from useless countries. Strcmp functions are meant to work around the silly PHP string comparison which inevitably tries compare strings as numbers when possible. I'll make no comment about that fact ... bit I have to bite my tong hard :
function PlageVersCIDRs($ip_min, $ip_max) {
$cidrs = array();
$ip_min_bin = sprintf('%032b', $ip_min);
$ip_max_bin = sprintf('%032b', $ip_max);
$ip_cour_bin = $ip_min_bin;
while (strcmp($ip_cour_bin, $ip_max_bin) <= 0) {
$lng_reseau = 32;
$ip_reseau_bin = $ip_cour_bin;
while (($ip_cour_bin[$lng_reseau - 1] == '0') && (strcmp(substr_replace($ip_reseau_bin, '1', $lng_reseau - 1, 1), $ip_max_bin) <= 0)) {
$ip_reseau_bin[$lng_reseau - 1] = '1';
$cidrs[] = long2ip(bindec($ip_cour_bin)).'/'.$lng_reseau;
$ip_cour_bin = sprintf('%032b', bindec($ip_reseau_bin) + 1);
return $cidrs;

03-apr-2003 05:11

Alternative cidr_conv function - a little easier to follow
function cidr_conv($cidr_address) {
 $first = substr($cidr_address, 0, strpos($cidr_address, "/"));
 $netmask = substr(strstr($cidr_address, "/"), 1);
 $first_bin = str_pad(decbin(ip2long($first)), 32, "0", STR_PAD_LEFT);
 $netmask_bin = str_pad(str_repeat("1", (integer)$netmask), 32, "0", STR_PAD_RIGHT);
 for ($i = 0; $i < 32; $i++) {
   if ($netmask_bin[$i] == "1")
     $last_bin .= $first_bin[$i];
     $last_bin .= "1";
 $last = long2ip(bindec($last_bin));
 return "$first - $last";


A simple and very fast function to check against CIDR.
Your previous examples are too complicated and involves a lot of functions call.
Here it is (only with arithmetic operators and call only to ip2long () and split() ):
 function ipCIDRCheck ($IP, $CIDR) {
   list ($net, $mask) = split ("/", $CIDR);
   $ip_net = ip2long ($net);
   $ip_mask = ~((1 << (32 - $mask)) - 1);
   $ip_ip = ip2long ($IP);
   $ip_ip_net = $ip_ip & $ip_mask;
   return ($ip_ip_net == $ip_net);
call example: <?php echo ipCheck ("", ""); ?>

... and this one will do the opposite (o return NULL for invalid netblocks) : -> -> ->
function ip2cidr($ip_start,$ip_end) {
if(long2ip(ip2long($ip_start))!=$ip_start or long2ip(ip2long($ip_end))!=$ip_end) return NULL;
if($ipl_start>0 && $ipl_end<0) $delta=($ipl_end+4294967296)-$ipl_start;
else $delta=$ipl_end-$ipl_start;
if(ip2long($ip_start)==0 && substr_count($netmask,"1")==32) return "";
if($delta<0 or ($delta>0 && $delta%2==0)) return NULL;
for($mask=0;$mask<32;$mask++) if($netmask[$mask]==1) break;
if(substr_count($netmask,"0")!=$mask) return NULL;
return "$ip_start/$mask";

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