core-bundle/src/Resources/contao/library/Contao/Environment.php
protected static function server()
	{
		$strServer = !empty($_SERVER['SERVER_ADDR']) ? $_SERVER['SERVER_ADDR'] : $_SERVER['LOCAL_ADDR'];

		// Special workaround for Strato users
		if (empty($strServer))
		{
			$strServer = @gethostbyname($_SERVER['SERVER_NAME']);
		}

		return $strServer;
	}
protected static function server()
	{
		$strServer = !empty($_SERVER['SERVER_ADDR']) ? $_SERVER['SERVER_ADDR'] : $_SERVER['LOCAL_ADDR'];

		// Special workaround for Strato users
		if (empty($strServer))
		{
			$strServer = @gethostbyname($_SERVER['SERVER_NAME']);
		}

		return $strServer;
	}
Return the SERVER_ADDR

@return string The IP address of the server