(PHP 4, PHP 5)
gethostbyaddr — Get the Internet host name corresponding to a given IP address
$ip_address
)
Returns the host name of the Internet host specified by
ip_address.
ip_address
The host IP address.
Returns the host name on success, the unmodified ip_address
on failure, or FALSE on malformed input.
Example #1 A simple gethostbyaddr() example
<?php
$hostname = gethostbyaddr($_SERVER['REMOTE_ADDR']);
echo $hostname;
?>
Mark in Sussex (2011-08-28 11:21:44)
If you use gethostbyaddr() with a bad IP address then it will send an error message to the error log.
If you don't want your error log file getting too big then first check that the IP address is valid.
In the following example I first check if the IP number starts with a number,
if not then don't use gethostbyaddr('..')
<?php
$IP = "BadValue.123.123.123";
if(intval($IP)>0){
$ServerIP = gethostbyaddr($IP);
} else {
$ServerIP = $IP; // A bad address.
}
?>
contact at muluweb dot net (2011-04-29 16:55:31)
If there are several host names for one IP address (many domain names can link to the same physical computer/server), gethostbyaddr() will return a domain name AT RANDOM.
I'm surprised it hasn't been said before.
You can try and see by yourself.
On some shared hosting services, it will not give you any domain name that is registered to that server (fortunately) but a general domain name referring to clusters.
Try it on your own server if it is referred by at least 2 domain names, if you have one.
james at trnxs dot net (2011-01-12 12:45:13)
You should be careful in the use of $_SERVER['HTTP_X_FORWARDED_FOR'], as I discovered, once using Amazon AWS's Elastic Load Balancer's, this value may be a comma separated list of IP addresses and will thusly not compare as conceived in almost every example I have seen posted by users in the comments.
dhjdhj at gmail dot com (2010-09-25 06:58:00)
I have observed that there are problems with all approaches that use the existence of an IP address to verify that the name being looked up actually exists.
If you're using opendns, then a request to a non-existent server returns an IP address anyway, the address being one for an opendns server. This is process is presumably in place so that errant URLs in browser requests take you to a "legitimate" page, i.e, the openDNS website where they can notify you of a problem.
Unfortunately, that mechanism seems to occur for ANY non-existent hostname. Appending a single period to the hostname does not seem to help.
Norf (2010-09-08 22:08:09)
The dns_get_record function seems to avoid timeout problems caused by gethostbyaddr() when looking up no existent records.
Example below.
<?php
function get_host($ip){
$ptr= implode(".",array_reverse(explode(".",$ip))).".in-addr.arpa";
$host = dns_get_record($ptr,DNS_PTR);
if ($host == null) return $ip;
else return $host[0]['target'];
}
print get_host('192.168.1.5');
?>
Stuart Macdonald (2010-08-28 05:07:08)
Here's a simple function that uses Dig to obtain the hostname for a given IP address. If no hostname can be found it returns the IP again.
Works only on linux / unix, or whatever other platform with dig installed as a command line utility.
<?php
function tryGetHost($ip)
{
$string = '';
exec("dig +short -x $ip 2>&1", $output, $retval);
if ($retval != 0)
{
// there was an error performing the command
}
else
{
$x=0;
while ($x < (sizeof($output)))
{
$string.= $output[$x];
$x++;
}
}
if (empty($string))
$string = $ip;
else //remove the trailing dot
$string = substr($string, 0, -1);
return $string;
}
?>
tobobant at web dot de (2010-07-12 15:08:57)
DNS lookup on Win + Linux:
<?php
/*
* This function returns the real hostname of an ip address.
*
* @param: $ip - the ip address in format x.x.x.x where x are
* numbers (0-255) or the hostname you want to lookup
* @return: returns the hostname as string. Something like 'user-id.isp-dialin.tld'
*
* Warning: $ip must be validated before calling this function.
*/
function nslookup($ip) {
// execute nslookup command
exec('nslookup '.$ip, $op);
// php is running on windows machine
if (substr(php_uname(), 0, 7) == "Windows") {
return substr($op[3], 6);
}
else {
// on linux nslookup returns 2 diffrent line depending on
// ip or hostname given for nslookup
if (strpos($op[4], 'name = ') > 0)
return substr($op[4], strpos($op[4], 'name =') + 7, -1);
else
return substr($op[4], strpos($op[4], 'Name:') + 6);
}
}
// example function call to get hostname of user ip:
echo nslookup($_SERVER['REMOTE_ADDR']);
?>
rhj at rhj dot info (2009-11-25 12:27:04)
DNS lookup with timeout on a Mac:
<?php
function dns_timeout($ip)
{
$res=`nslookup -timeout=2 -retry=1 $ip`;
if (preg_match('/name = (.*).\n/', $res, $out))
{
return $out[1];
} else
{
return $ip;
}
}
?>
marco[DOT]ceppi[@T]seacrow[DOT]org (2009-11-01 07:24:19)
Anonymous has a good point (though I don't agree with pushing to execution to shell unless I have to. However this is a faster example (explode then loop is a little too intensive for a simple check)
<?php
function gethost ($ip)
{
//Make sure the input is not going to do anything unexpected
//IPs must be in the form x.x.x.x with each x as a number
if( preg_match('/^(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)(?:[.]
(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)){3}$/', $ip) )
{
$host = `host $ip`;
return (($host ? end ( explode (' ', $host)) : $ip));
}
else
{
return false;
}
}
?>
Though to be honest I would use:
<?php
function gethost ($ip)
{
return ( preg_match('/^(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)(?:[.]
(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)){3}$/', $ip) ) ? gethostbyaddr($ip) : false;
}
?>
job4sap at gmail dot com (2009-04-29 11:27:26)
I have added a file php.ini in the same directory with the entries I use for other scripts. I think that the first one does the trick and solved the problem.
register_globals = on
session.bug_compat_42 = off
session.bug_compat_warn = off
Anonymous (2009-04-02 11:39:01)
The use of the shell command to speed things up seems to work very well, but I would suggest one thing: you ARE executing a shell command, so it would seem to be a good idea to be absolutely sure of your input. Something like this perhaps:
<?php
function gethost ($ip)
{
//Make sure the input is not going to do anything unexpected
//IPs must be in the form x.x.x.x with each x as a number
$testar = explode('.',$ip);
if (count($testar)!=4)
return $ip;
for ($i=0;$i<4;++$i)
if (!is_numeric($testar[$i]))
return $ip;
$host = `host $ip`;
return (($host ? end ( explode (' ', $host)) : $ip));
}
?>
Anonymous (2009-02-13 02:07:31)
Just wanted to let everyone know that gethostbyaddr() takes more than 20 seconds to respond if the IP address is not listed in DNS.
So be careful if you are going to use this function in the production environment. You or your users may not be able to get the response from the server before the timeout occurs. Slow website only makes people very frustrated.
You shouldn't use this function at all unless you have a very good reason to do so (taking logs? then save ip addresses instead and resolve them later by running a batch or something.)
webmaster at askapache dot com (2008-10-22 01:57:46)
Here is a simple function I compiled from user-notes that works great.. any improvements?
<?php
function get_ip( $host ){
$hostip = @gethostbyname( $host );
$ip = ( $hostip == $host ) ? $host : long2ip( ip2long( $hostip ) );
//echo sprintf("Resolved %s to %s", $host, $ip);
return $ip;
}
?>
robbakAgmail_com (2008-06-05 23:19:14)
it appears that gethostbyname() fails if the domain name contains unicode. Example:
$ host 10.10.10.128
128.10.10.10.in-addr.arpa domain name pointer PC-de-S\130bastien.flexi.robbak.com.
$ php
<?php echo gethostbyaddr( '10.10.10.128' ); ?>
10.10.10.128
gethostbyaddr is listed as unicode compatable in version 6, so a fix may be in the works.
ab5602 at php dot net (2008-01-28 16:39:32)
gethostbyaddr() will not resolve an IP under Solaris for hosts that do not both forward and reverse to the same address. This is built-in Solaris behavior, not a bug in PHP.
billyblue (2007-12-17 20:12:52)
I just spent a dickens of a time trying to figure out why my gethostbyaddr's were simply failing halfway through.
I'm returning a log of page visits, and with each new IP, I wanted to pull the hostname of the IP. On each report page, I'm pulling 500 lines from my Db, but only maybe 25 IPs on average. Sometimes this report would generate in under 15 seconds, other times it would fail with a connection reset.
It turns out that several of the IPs in my Db looked like this: x.255.x.x. gethostbyaddr really hates that and simply dies when it reaches one of these IPs.
For my case, I purged the Db and prevented the logging of IPs that contain 255.
CanYouFlyBilly (2006-04-17 14:08:57)
Just wanted to contribute for the solaris folks out there that don't have "host" installed. This will return the resolved named of the specified ip address if it exist.
NOTE: The " " in the explode statement should be a tab character. explode was used instead of preg_split in order to eliminate regular expression overhead.
<?
function gethost($ipaddress)
{
$host = trim( `getent hosts $ipaddress` );
$host=explode(" ",$host);
if(isset($host[1])) return $host[1];
else return "";
}
?>
oryan at zareste dot com (2006-02-28 15:17:05)
If all else fails, but you have shell access, Unix/Linux servers can use this for a timeout response:
shell_exec('host -W 2 0.0.0.0');
Where 0.0.0.0 is of course the IP, and '2' is the number of seconds for the timeout. This returns a more detailed string of info, with some additional text which might vary depending on the system, so if you want a string with the hostname and nothing else, you'll have to do some substring cutting. There should be an equivalent of 'host' for Windows users to execute, but it isn't my platform.
Rathann (2006-02-26 09:51:48)
While writing a script to verify IP<->hostname loops, I sorely missed the "list" version of gethostbyaddr (similar to gethostbynamel()) and since dns_get_record is a bit too complex for that task alone, I've written a simple wrapper that should behave like gethostbynamel():
function gethostbyaddrl($ip) {
$rrs=dns_get_record(implode('.',array_reverse(explode('.', $ip))).'.in-addr.arpa.',DNS_PTR);
$revnames=array();
foreach($rrs as $rr) $revnames[]=$rr['target'];
return (count($revnames)) ? $revnames : FALSE;
}
Hopefully it'll be of use to someone else, too.
respaldod at gmail dot com (2005-11-22 10:28:36)
There is a small flaw in the timeout implementation of King Macro's very useful sockets-based function gethostbyaddr_timeout() below.
The parameters for socket_set_timeout, an alias for stream_set_timeout(), are like this:
( resource stream, int seconds [, int microseconds] )
So if you want to use his parameters, and assuming the $timeout param should be in milliseconds, you could first convert to microseconds
$timeout *= 1000;
And then change the socket_set_timeout so you have seconds and microseconds along these lines:
@socket_set_timeout($handle, floor($timeout/1000000), $timeout%1000000);
tom (2005-10-07 01:14:45)
Be careful with the usage of this function - it will slow down a server to a crawl if called a lot and the slowness won't be reflected in any of the obvious places, like CPU usage, apache requests, SQL etc. When you do use it make a special note of where!
reinhard at ess dot co dot at (2005-04-12 02:27:19)
tried out some of the examples below, but no one worked for me.
(
"host" returns something if domain-name wasn't found
"gethostbyaddr" has a too long timeout when it fails
"the udp-example" returns some strange characters...
)
so i have changed the "host"-example a little bit. hope someone can need it. (maybe with little changes like without error-description)
<?
function gethost($ip)
{
$host = `host $ip`;
$host=end(explode(' ',$host));
$host=substr($host,0,strlen($host)-2);
$chk=split("\(",$host);
if($chk[1]) return $ip." (".$chk[1].")";
else return $host;
}
?>
king dot macro at gmail dot com (2004-10-26 07:28:24)
The problem of broken DNS servers was causing me a problem because i had a page for user statistics that required around 20 reverse dns lookups to be done, and even as many as 5/6 of them being broken was causing a huge delay in loading the page. so i wrote a function that uses a UDP socket to talk directly to the DNS server (instead of going via the normal gethostbyaddr function) this let me set a timeout.
The only requirement is that your DNS server must be able to do recursive lookups, it wont go to other DNS servers if its told to... and of course you need to know your DNS servers IP address :-)
<?
function gethostbyaddr_timeout($ip, $dns, $timeout=1000)
{
// random transaction number (for routers etc to get the reply back)
$data = rand(0, 99);
// trim it to 2 bytes
$data = substr($data, 0, 2);
// request header
$data .= "\1\0\0\1\0\0\0\0\0\0";
// split IP up
$bits = explode(".", $ip);
// error checking
if (count($bits) != 4) return "ERROR";
// there is probably a better way to do this bit...
// loop through each segment
for ($x=3; $x>=0; $x--)
{
// needs a byte to indicate the length of each segment of the request
switch (strlen($bits[$x]))
{
case 1: // 1 byte long segment
$data .= "\1"; break;
case 2: // 2 byte long segment
$data .= "\2"; break;
case 3: // 3 byte long segment
$data .= "\3"; break;
default: // segment is too big, invalid IP
return "INVALID";
}
// and the segment itself
$data .= $bits[$x];
}
// and the final bit of the request
$data .= "\7in-addr\4arpa\0\0\x0C\0\1";
// create UDP socket
$handle = @fsockopen("udp://$dns", 53);
// send our request (and store request size so we can cheat later)
$requestsize=@fwrite($handle, $data);
@socket_set_timeout($handle, $timeout - $timeout%1000, $timeout%1000);
// hope we get a reply
$response = @fread($handle, 1000);
@fclose($handle);
if ($response == "")
return $ip;
// find the response type
$type = @unpack("s", substr($response, $requestsize+2));
if ($type[1] == 0x0C00) // answer
{
// set up our variables
$host="";
$len = 0;
// set our pointer at the beginning of the hostname
// uses the request size from earlier rather than work it out
$position=$requestsize+12;
// reconstruct hostname
do
{
// get segment size
$len = unpack("c", substr($response, $position));
// null terminated string, so length 0 = finished
if ($len[1] == 0)
// return the hostname, without the trailing .
return substr($host, 0, strlen($host) -1);
// add segment to our host
$host .= substr($response, $position+1, $len[1]) . ".";
// move pointer on to the next segment
$position += $len[1] + 1;
}
while ($len != 0);
// error - return the hostname we constructed (without the . on the end)
return $ip;
}
return $ip;
}
?>
This could be expanded quite a bit and improved but it works and i've seen quite a few people trying various methods to achieve something like this so i decided to post it here. on most servers it should also be more efficient than other methods such as calling nslookup because it doesn't need to run external programs
Note: I'm more a C person than a PHP person, so just ignore it if anything hasn't been done the *recomended* way :-)
MagicalTux at FF.ST (2004-03-15 10:58:17)
Note that sometime, people have broken DNS...
I mean that the IP resolve to a domain, but the reverse-resolution don't give the same IP.
I did a local test, putting a PTR record on my dns server to say 192.168.0.1 resolv to php.net . When calling gethostbyaddr, I saw "Your host is php.net" ... So when you log the DNS names, you have two options :
- Log the IP adresses to prevent fake ips
- Call gethostbyname on the result and verify that the IP is really the initial IP.
Note that not everyone can do that, only people with control on their own ip classes... Once, on the real net, I got an IP resolving to "PROGRAM". It was obviously a fake record.
Note 2 for windows users : I noticed that some software takes the reverse record as athoritative. It may allow people to do fake DNS entries if you do the reverse dns on your host. The best is to only log IPs. Imagine someone with an host resolving to www.paypal.com. Next time you try to access paypal, you will be redirected to his/her IP without even knowing it. Also faking update servers for antivirus software, or winamp (there was a thread regarding this security problem because of a problem in winamp updater if the remote server was faked) will be concerned.
Matt AKA Junkie (2004-03-14 20:29:40)
Going through numerous tests, the following results are concluded:
<?
// If you're using a server on Windows, this is faster
function getisp($ip='') {
if ($ip=='') $ip = $_SERVER['REMOTE_ADDR'];
$longisp = @gethostbyaddr($ip);
$isp = explode('.', $longisp);
$isp = array_reverse($isp);
$tmp = $isp[1];
if (preg_match("/\<(org?|com?|net)\>/i", $tmp)) {
$myisp = $isp[2].'.'.$isp[1].'.'.$isp[0];
} else {
$myisp = $isp[1].'.'.$isp[0];
}
if (preg_match("/[0-9]{1,3}\.[0-9]{1,3}/", $myisp))
return 'ISP lookup failed.';
return $myisp;
}
// If your server is on a *nix system, this is faster
function gethost ($ip) {
$host = `host $ip`;
return (($host ? end ( explode (' ', $host)) : $ip));
}
// be warned, however, that gethost() will issue a warning
// if safe mode is on with the use of backticked variables
?>
webmaster at script-tease dot net (2004-03-14 04:37:03)
gethostbyaddr() tends to lag on various systems for whatever reason. Here are two functions that should prove their worth speedwise.
<?php
// For Linux...
function gethost ($ip) {
$host = `host $ip`;
return (($host ? end ( explode (' ', $host)) : $ip));
}
// For Win32...
function nslookup ($ip) {
$host = split('Name:',`nslookup $ip`);
return ( trim (isset($host[1]) ? str_replace ("\n".'Address: '.$ip, '', $host[1]) : $ip));
}
?>
Pretty basic, but it should get the job done.
Matt AKA Junkie (2004-02-29 16:11:53)
Since my little ISP thing isn't globally acceptable, here's an update.
<?
function getisp($ip='') {
if ($ip=='') $ip = $_SERVER['REMOTE_ADDR'];
$longisp = @gethostbyaddr($ip);
$isp = explode('.', $longisp);
$isp = array_reverse($isp);
$tmp = $isp[1];
if (preg_match("/\<(org?|com?|net)\>/i", $tmp)) {
$myisp = $isp[2].'.'.$isp[1].'.'.$isp[0];
} else {
$myisp = $isp[1].'.'.$isp[0];
}
preg_match("/[0-9]{1,3}\.[0-9]{1,3}/", $myisp) ? return 'ISP lookup failed.' : return $myisp;
}
?>
info at widebore dot com (2003-08-18 01:49:03)
Some users (a minority) will present IP addresses to the browser which cause problems with gethostbyaddr. I had a complaint from a user today about this.
This gives an error "Warning: Address is not in a.b.c.d form" and if you try to send any headers after this error has been generated, then, naturally, the results are unpleasant on the user's screen.
The simplest way I found to get round this problem which affects less than 1% of users is to put a "@" in front of gethostbyaddr and not lose any more sleep over it :-)
grimNOSPAMtraffic at hotNOSPAMmail dot com (2003-07-31 14:31:34)
If you have found the host of the ip, the shortest way to cut it not to display the full hostname to the public would be:
$host = substr($host, strpos($host, ".") + 1);
P.S. strpos() can also be easily used if you want to put "*" for every simbol you ommit, like so:
$os = strpos($host, ".");
$host = substr($host, $os);
$host = str_repeat("*", $os) . $host;
--McTrafik
www.ad-rotator.com (2003-04-28 16:06:24)
For ad-rotator.com, we need to do a lot of IP lookups, gethostbyaddr is very easy get timed-out and the script stucks there forever. Here is a fail-safe alternative, 1 sec max for timeout per IP.
function ar_gethostbyaddr($ip) {
$output = `host -W 1 $ip`;
if (ereg('.*pointer ([A-Za-z0-9.-]+)\..*',$output,$regs)) {
return $regs[1];
}
return $ip;
}
jz at NOSPAM dot nplu dot kiev dot ua (2003-04-11 03:59:08)
Just to fun that gethostbyadd() returns server machine name known in LAN rather then its DNS if I try to call it against my own host (from workstation), whether it would local (behind the proxy) or global (of proxy itself) IP or just loop 127.0.0.1.
And thus you can get LAN names of other workstations by its intranet IPs (I mean smth like 192.168.0.???)
Fun :)
kriek at jonkriek dot com (2003-03-21 08:39:54)
In response to god at weaponzero dot f2s dot com: I found this much easier to write.
<?php
$ip = $_SERVER['REMOTE_ADDR'];
$fullhost = gethostbyaddr($ip);
$host = preg_replace("/^[^.]+./", "*.", $fullhost);
?>
IP address <?=$ip?> | Host: <?=$host?>
You can still protect the IP of your visitors and only show the hostname or show them both.
root don't send spam to em411 dot com (2003-02-07 10:01:06)
recently, i've encountered a bad experience with this function. while i have yet to find out the root of the problem, i would like to share my experience.
i woke up one morning to find all pages on my server loading very slowly. frontpage load speed is typically .4seconds, and that morning, it was 12seconds. after 24 hours of myisamchk'ing, top / ping / tracert / reboot / service mysqld / httpd restartin'ing, nothing helped. eventually, i tracked the bugger down to the gethostbyaddr function.
the anomaly was that the problem was only happening to ME, and not to my 1-200 users per day.
would love to hear suggestion on why this happened and potential resolutions, if any exist. thank you.
webmaster at 4so9 dot com (2002-12-25 10:12:33)
I could never get one host name from this function. I have even tried to turn on "HostnameLookup On" w/o success. I have combined all your your advises into this piece of codes. Any help on this is greatly appreciated.
------
function getRemoteInfo () {
$proxy="";
$IP = "";
if (isSet($_SERVER)) {
if (isSet($_SERVER["HTTP_X_FORWARDED_FOR"])) {
$IP = $_SERVER["HTTP_X_FORWARDED_FOR"];
$proxy = $_SERVER["REMOTE_ADDR"];
} elseif (isSet($_SERVER["HTTP_CLIENT_IP"])) {
$IP = $_SERVER["HTTP_CLIENT_IP"];
} else {
$IP = $_SERVER["REMOTE_ADDR"];
}
} else {
if ( getenv( 'HTTP_X_FORWARDED_FOR' ) ) {
$IP = getenv( 'HTTP_X_FORWARDED_FOR' );
$proxy = getenv( 'REMOTE_ADDR' );
} elseif ( getenv( 'HTTP_CLIENT_IP' ) ) {
$IP = getenv( 'HTTP_CLIENT_IP' );
} else {
$IP = getenv( 'REMOTE_ADDR' );
}
}
if (strstr($IP, ',')) {
$ips = explode(',', $IP);
$IP = $ips[0];
}
$RemoteInfo[0]=$IP;
$RemoteInfo[1]=@GetHostByAddr($IP);
$RemoteInfo[2]=$proxy;
return $RemoteInfo;
}
-------
Thanks,
Steve
lukevb_at_iafrica.com (2002-11-09 02:43:13)
Sometimes when using $_SERVER['HTTP_X_FORWARDED_FOR'] OR $_SERVER['REMOTE_ADDR'] more than 1 IP address is returned, for example '155.240.132.261, 196.250.25.120'. When this string is passed as an argument for gethostbyaddr() PHP gives the following error: Warning: Address is not a valid IPv4 or IPv6 address in...
To work around this I use the following code to extract the first IP address from the string and discard the rest. (If you wish to use the other IPs they will be in the other elements of the $ips array).
if (strstr($remoteIP, ', ')) {
$ips = explode(', ', $remoteIP);
$remoteIP = $ips[0];
}
Hope this helps someone :)
abe at abe2k dot net (2002-11-07 18:32:59)
gethostbyaddr() doesn't seem to be able to resolve ip6.int
(ipv6) adresses, so I made a function that can, and works
just like the normal gethostbyaddr().
You need dig and ipv6calc, dig should come with most
distributions, if not, install bind from http://www.isc.org.
ipv6calc can be found at http://www.bieringer.de/linux/IPv6/ipv6calc/index.html.
function gethostbyaddr6($ip6) {
$ipv6calc = "/bin/ipv6calc";
$dig = "/usr/bin/dig";
$file = popen($ipv6calc." --in ipv6addr --out revnibbles.int ".escapeshellarg($ip6), r);
$ip = fread($file, 128);
pclose($file);
if ((substr($ip, 0, 5) == "Error") || (!$ip)) return "Address is not a valid IPv6 address";
$file = popen($dig." ptr ".$ip, r);
while (!feof ($file)) {
$buffer = fgets($file, 128);
if (substr($buffer, 0, 1) == ";") continue;
$buffer = explode(" ", $buffer);
if ($buffer[3] == "PTR") {
$host = substr(trim($buffer[4]), 0, -1);
pclose($file);
return $host;
}
}
pclose($file);
return $ip6;
}
echo gethostbyaddr6($_SERVER[REMOTE_ADDR]);
ameoba32 at mail dot ru (2002-11-01 04:29:36)
DNS lookup with timeout
function dns_timeout($ip) {
$res=`nslookup -timeout=3 -retry=1 $ip`;
if (preg_match('/\nName:(.*)\n/', $res, $out)) {
return trim($out[1]);
} else {
return $ip;
}
}
dominique at vdx dot nl (2002-09-30 05:14:07)
To convert an IP to a numeric value, just use the ip2long (...) function.
Vice versa; use: long2ip (...)
pulstar at mail dot com (2002-09-20 14:59:52)
If you need to store an IP addresses in a database, you can convert and store it in an INT type column (4 bytes). The functions below can convert IP addresses to its integer decimal value and vice-versa.
function ip2dec($ipaddr) {
$base=explode(".",$ipaddr);
$decimal=(double) $base[0]*16777216;
$decimal+=$base[1]*65536;
$decimal+=$base[2]*256;
$decimal+=$base[3];
if($decimal>2147483647) {
$decimal-=4294967296;
}
return (int) $decimal;
}
function dec2ip($dec) {
if($dec<0) {
$dec=(double) 4294967296+$dec;
}
if($dec>16777215) {
$ip=$dec-(intval($dec/256)*256);
$dec=(double) intval($dec/256);
} else $ip="0";
if($dec>65535) {
$ip=($dec-(intval($dec/256)*256)).".".$ip;
$dec=(double) intval($dec/256);
} else $ip="0.".$ip;
if($dec>255) {
$ip=($dec-(intval($dec/256)*256)).".".$ip;
$dec=(double) intval($dec/256);
} else $ip="0.".$ip;
$ip=$dec.".".$ip;
return (string) $ip;
}
alexey at ozerov dot de (2002-09-15 10:15:05)
This function seems to be very slow on IIS 4.0 Server (Win32). I use system call to NSLOOKUP instead to get PC-Hostname:
unset ($execoutput);
exec ("nslookup $IPAdresse 2>nul",$execoutput,$nslookstatus);
if (isset ($execoutput[3]) && ereg ("^Name: *([A-Za-z0-9]{2,})\.",$execoutput[3],$regs))
$nslookname=strtoupper($regs[1]);
else $nslookname="Unknown";
Note by members: This is not portable to Windows platforms. so you would be better to stay with our function.
stephane at metacites dot net (2002-09-10 07:17:17)
gethostbyaddr_with_cache()
As someone truely said upper in the forum, some unresolved addresses may slow down your script to the point it times out.
Althought I had thought gethostbyaddr() would use some kind of cache, it doesn't seem to when the IP is unresolved (at least on my win machine).
So, I've coded a little gethostbyaddr_with_cache() function that will greatly speed your page if you have many gethostbyaddr() to perform on the same page.
function gethostbyaddr_with_cache($a) {
global $dns_cache;
if ($dns_cache[$a]) {
return $dns_cache[$a];
} else {
$temp = gethostbyaddr($a);
$dns_cache[$a] = $temp;
return $temp;
}
}
inny at core dot fetchnet dot org (2002-08-10 09:58:06)
Turning on the HostnameLookup function on in the apache configuration file will severely increase the loading times of all the pages serviced by the httpd-server.
It's mostly a better idea to just use gethostbyaddr($REMOTE_ADDR); instead of $REMOTE_HOST if you turned HostnameLookups On, unless you want the hostnames specified in apache's log file...
ven at PragaKhan dot com (2002-07-16 03:55:59)
$REMOTE_HOST or $_SERVER['REMOTE_HOST'] will give you the reversed ip IF apache is setup to do hostname lookups.
HostnameLookups On
elpmille at indiana dot edu (2002-05-30 00:26:35)
I previously used something very similar to what god@weaponzero.f2s.com posted but found it to be quite tedious for getting the 'nicehost'. This method below is a lot cleaner, and it also works for numeric addresses.
function nicehost($host) {
if (ereg('^([0-9]{1,3}\.){3}[0-9]{1,3}$', $host)) {
return(ereg_replace('\.[0-9]{1,3}$', '.*', $host));
} else {
return(ereg_replace('^.{' . strpos($host, '.') . '}', '*', $host));
}
}
nothanks at nospam dot com (2002-05-16 15:30:01)
This is also very useful if you'd like to ban these annoying people that keep spamming your forums. It requires a clever use of mySql but can be great:
First, make a table for the bans, then make the query:
"SELECT banReason from tBans where '". gethostbyaddr($REMOTE_ADDR) ."' LIKE banMask"
If your results aren't null it means his host matched a banMask in your DB, so you can redirect him with header() to a banned.php page and prevent him from accessing any content on your page!
phalkon at nospam dot home dot com (2001-06-08 15:58:30)
Be cautious when looking up many hostnames. If your DNS server is slow to respond, you may have to pump up your Max execution time for your scripts, otherwise, it will timeout. I found that even 3 unresolvable hosts can cause a 30 second delay in processing.
andy at occ dot nu (2001-01-12 06:48:43)
if the user is sitting behind a proxy server, you can do this;
<?
if ($HTTP_SERVER_VARS["HTTP_X_FORWARDED_FOR"] != ""){
$IP = $HTTP_SERVER_VARS["HTTP_X_FORWARDED_FOR"];
$proxy = $HTTP_SERVER_VARS["REMOTE_ADDR"];
$host = @gethostbyaddr($HTTP_SERVER_VARS["HTTP_X_FORWARDED_FOR"]);
}else{
$IP = $HTTP_SERVER_VARS["REMOTE_ADDR"];
$host = @gethostbyaddr($HTTP_SERVER_VARS["REMOTE_ADDR"]);
}
?>
ps; i use $HTTP_SERVER_VARS["something"] instead of just $something;
you can get most of the $HTTP_SERVER_VARS by just using there $something equivalent, see the manual for that (preserved variables)
bruno at angelsp dot org (2000-11-22 18:20:11)
This is a really usefull function.. I ussualy use it to know the name of the country that the host has.. (.pt, .es, .uk, etc)..
here is a litle idea of what one can do with this..
I get the $ipa with the remote_addr function..
<?php
$host = gethostbyaddr($ipa);
$at = $host
$hostdot = ".";
$result = strrchr($at, $hostdot);
echo "The country is $result";
?>
Of course, if a .com or .org or .net domain name (tld) it won't be a country.. but you can work that out with and if or case statements..
and of course, I can be totally mistaken ;P