IP address from domain name by gethostbyname, gethostbyaddr() function

Resolve a host and verify the result

gethostbyname() returns the original hostname when resolution fails. Compare the return value and validate the resulting address before using it. Do not treat DNS resolution alone as authorization to connect to arbitrary user-supplied hosts.

<?php
$host = 'www.example.com';
$ip = gethostbyname($host);

if ($ip === $host || filter_var($ip, FILTER_VALIDATE_IP) === false) {
    echo 'Host could not be resolved.';
} else {
    echo htmlspecialchars($ip, ENT_QUOTES, 'UTF-8');
}
?>

We can get the ip address of the host server by using the domain name. For example we want to know the ip address of google.com. We can use the PHP function gethostbyname(). This function takes the domain name as input and return the dot formatted IPv4 address. Note that this function will contact DNS server so available network must be healthy at the time of running of the script. Let us try the function first.

$result = gethostbyname('plus2net.com');
echo $result;

This is the ip address of the host server of plus2net.com.

Gethostbyaddr()

Now from this information we can find out the domain name by using another function gethostbyaddr(). This function will take ip address as input and return the domain name. Let us add the above two functions and see what happens if out put of one function is used as input to other. Here is the code.

$result = gethostbyname('plus2net.com');
echo $result;
echo "<br>";
echo gethostbyaddr($result);

The output of the above code is

74.53.25.146
4runner.websitewelcome.com

Gethostbynamel()

This function gives us more information. It returns an array with all the details. To display this array we will use print_r function. Here is the code.

$result = gethostbynamel('google.com');
print_r($result);

The output of above code is here

Array ( [0] => 74.125.67.100 [1] => 74.125.127.100 [2] => 74.125.45.100 )

Example: Validating Domain Name

$domain = "example.com";
$ip = gethostbyname($domain);
if ($ip === $domain) {
    echo "Invalid domain or no IP found.";
} else {
    echo "Domain resolves to: " . $ip;
}

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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Gethostbyname function to get IP name of a domain

Resolve a host and verify the result

Gethostbyaddr()

Gethostbynamel()

Example: Validating Domain Name

Subhendu Mohapatra