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From IP address, extract just the first three octets (network) from the address using PHP

Posted on 2006-06-22
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Last Modified: 2008-02-01
I want to extract just the first three octets (the network basically) from an IP address with PHP.

I have an IP address (i.e.  1.2.3.4)
and I want to extract just the:   1.2.3    part

It could be 1, 2 or 3 numbers per octet (since it's an IP address):
   could be:             I want:
  192.168.0.1   -->  192.168.0
  10.1.102.3    -->   10.1.102

etc.

Thanks.
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Question by:ldorazio
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b0lsc0tt earned 250 total points
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ldorazio,

if (strrpos($ip, ".") != False) {
  $strIp = substr($ip, 0, strrpos($ip, "."));
}

In the example above $ip is the ip address.  The function strrchr() will look for the last occurrance of the period.  If it is not found then it will return false so that is why I have the If statement.  If it finds a period in $ip then it will use the position of the last one to get a substring and assign it to $strIp.  If $ip was 192.168.1.100 then $strIp would be 192.168.1

b0lsc0tt
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by:Zyloch
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Hi ldorazio,

Well, since there are always at least three parts, you can just do:

$ip = '192.168.0.1';
$cut_ip = substr($ip, 0, strrpos($ip, '.'));
echo($cut_ip);

Regards,
Ted
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by:Zyloch
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Heh, didn't see your post, b0lsc0tt. My bad.

Ted
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by:b0lsc0tt
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@Zyloch - No problem!  I have been on the other side often too.  Posted at essentially the same time and I have no problem splitting if our answers help him.

bol
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by:Zyloch
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Don't worry about the split. The points are rightfully yours, and I don't care so much for them anyhow :P It's interesting how our answers are essentially the same though, hehe

Ted
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by:b0lsc0tt
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@Zyloch, I was not watching what you typed! :D  With your expertise in this area I am glad to see your similar post.  I'll be fine with whatever Idorazio decides to do regarding points.

bol
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by:RQuadling
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Silly idea, but ... (untested) ...

<?php
$s_ip = '192.168.0.1';
$i_ip = ip2long($s_ip);
$i_ip = $i_ip & ~255;
$s_ip = long2ip($i_ip);
$s_ip = substr($s_ip, 0, -2);
?>

Take the string. Convert it to a long using ip2long(). Mask off the lower 8 bits. Convert it back to an IP which will now end in ".0". Substr to drop off the last 2 characters.

I doubt I'd actually do it this way, but an exercise all the same.

And at least it is actually using a mask! So MAYBE has more relevance than just string manipulation.

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by:ldorazio
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Awesome, thank you!

Sometimes I can't think the right way, and I was in a hurry so I appreciate the quick answers.
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by:RQuadling
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A completely useless example of masking. I had a spare 10 mins whilst a backup was running.

<?php
function maskIP($s_IP, $i_bits)
      {
      $i_IP = ip2long($s_IP);
      $i_mask = ($i_bits > 0) ? pow(2, $i_bits) - 1 : 0;
      $i_IP &= ~$i_mask;
      $s_IP = long2ip($i_IP);
      return $s_IP;
      }

$s_IP = rand(0, 255) . '.' . rand(0, 255) . '.' . rand(0, 255) . '.' . rand(0, 255);
$i_mask = rand(0, 32);
echo $s_IP . ' mask ' . $i_mask . ' is ' . maskIP($s_IP, $i_mask) . "\n";
?>
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by:b0lsc0tt
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Your welcome!  I'm glad that I could help you and I enjoyed participating with the others in this.  Thank you for the grade, the points and the fun question.

bol
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