The PHP checkdnsrr() function checks DNS records for type corresponding to host, and can be used to check our DNS record to verify a domain’s existence.

The PHP closelog() function closes the connection of system logger.

The PHP dns_check_record() function is an alias of the checkdnsrr() function.

The PHP dns_get_mx() function is an alias of the getmxrr() function.

The PHP dns_get_record() function gets the DNS resource records associated with the specified hostname.

The PHP fsockopen() function opens an Internet or Unix domain socket connection.

The PHP gethostbyaddr() function returns the domain name for a given IP address.

The PHP gethostbyname() function returns the IPv4 address for a given domain/host name.

The PHP gethostbynamel() function returns a list of IPv4 address for a given domain/host name.

The PHP gethostname() function returns the host name for the local machine.

The PHP getmxrr() function returns the MX records for the specified internet host name.

The PHP getprotobyname() function returns the protocol number for a given protocol name.

The PHP getprotobynumber() function returns the protocol name for a given protocol number.

The PHP getservbyname() function returns the port number for a given Internet service and protocol.

The PHP getservbyport() function returns the Internet service for a given port and protocol.

The PHP header() function sends a raw HTTP header to a client, and must be called before any actual output is sent.

The PHP header_register_callback() function calls a header function to be executed after all PHP headers are sent, and before any other output is sent.

The PHP header_remove() function removes an HTTP header previously set with the header() function.

The PHP headers_list() function returns a list of response headers to be sent to the browser.

The PHP headers_sent() function checks if/where headers have been sent.