How to resolve a hostname or FQDN to an IP address Using PHP

In PHP, resolving a hostname or Fully Qualified Domain Name (FQDN) to an IP address is a common requirement in networked applications. This process involves converting a domain name, such as example.com, into its associated IP address. PHP offers built-in functions that handle this task efficiently.

The gethostbyname() function is typically used to convert a hostname into its IPv4 address. It provides a direct way to obtain a single IP address for a given domain. For scenarios where multiple IP addresses are associated with a hostname, the gethostbynamel() function returns an array of all available IPv4 addresses.

To support both IPv4 and IPv6 addresses, the dns_get_record() function is used. This function allows you to retrieve specific types of DNS records, such as A (IPv4) and AAAA (IPv6) records. These functions provide the necessary tools to manage DNS resolutions in PHP applications.

1. Use gethostbyname() to resolve a hostname or FQDN to an IPv4 address.

   $hostname = "example.com";
   $ip_address = gethostbyname($hostname);
   echo "IP Address for $hostname: " . $ip_address;

2. If you need to retrieve multiple IP addresses, use gethostbynamel().

   $hostname = "example.com";
   $ip_addresses = gethostbynamel($hostname);
   if ($ip_addresses !== false) {
       foreach ($ip_addresses as $ip) {
           echo "IP Address: " . $ip . "\n";
       }
   } else {
       echo "Failed to resolve hostname.";
   }

3. To resolve both IPv4 and IPv6 addresses, use dns_get_record() and specify the desired DNS record type.

   $hostname = "example.com";
   $dns_records = dns_get_record($hostname, DNS_A + DNS_AAAA);
   foreach ($dns_records as $record) {
       if ($record['type'] === 'A' || $record['type'] === 'AAAA') {
           echo "IP Address: " . $record['ip'] . "\n";
       }
   }