只是个VB。NET版的答案:

Private Function GetRequestIpAddress() As IPAddress
    Dim serverVariables = HttpContext.Current.Request.ServerVariables
    Dim headersKeysToCheck = {"HTTP_CLIENT_IP", _
                              "HTTP_X_FORWARDED_FOR", _
                              "HTTP_X_FORWARDED", _
                              "HTTP_X_CLUSTER_CLIENT_IP", _
                              "HTTP_FORWARDED_FOR", _
                              "HTTP_FORWARDED", _
                              "REMOTE_ADDR"}
    For Each thisHeaderKey In headersKeysToCheck
        Dim thisValue = serverVariables.Item(thisHeaderKey)
        If thisValue IsNot Nothing Then
            Dim validAddress As IPAddress = Nothing
            If IPAddress.TryParse(thisValue, validAddress) Then
                Return validAddress
            End If
        End If
    Next
    Return Nothing
End Function

只是个VB。NET版的答案:

Private Function GetRequestIpAddress() As IPAddress
    Dim serverVariables = HttpContext.Current.Request.ServerVariables
    Dim headersKeysToCheck = {"HTTP_CLIENT_IP", _
                              "HTTP_X_FORWARDED_FOR", _
                              "HTTP_X_FORWARDED", _
                              "HTTP_X_CLUSTER_CLIENT_IP", _
                              "HTTP_FORWARDED_FOR", _
                              "HTTP_FORWARDED", _
                              "REMOTE_ADDR"}
    For Each thisHeaderKey In headersKeysToCheck
        Dim thisValue = serverVariables.Item(thisHeaderKey)
        If thisValue IsNot Nothing Then
            Dim validAddress As IPAddress = Nothing
            If IPAddress.TryParse(thisValue, validAddress) Then
                Return validAddress
            End If
        End If
    Next
    Return Nothing
End Function

谢谢，非常有用。

如果代码在语法上是正确的，这将会有所帮助。在第20行有一个{too many。这恐怕意味着没人真正尝试过。

我可能疯了，但在尝试了一些有效和无效的地址后，validate_ip()唯一有效的版本是这样的:

    public function validate_ip($ip)
    {
        if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE) === false)
            return false;
        if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_RES_RANGE) === false)
            return false;
        if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4) === false && filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6) === false)
            return false;

        return true;
    }

来自Symfony的Request类 https://github.com/symfony/symfony/blob/1bd125ec4a01220878b3dbc3ec3156b073996af9/src/Symfony/Component/HttpFoundation/Request.php

const HEADER_FORWARDED = 'forwarded';
const HEADER_CLIENT_IP = 'client_ip';
const HEADER_CLIENT_HOST = 'client_host';
const HEADER_CLIENT_PROTO = 'client_proto';
const HEADER_CLIENT_PORT = 'client_port';

/**
 * Names for headers that can be trusted when
 * using trusted proxies.
 *
 * The FORWARDED header is the standard as of rfc7239.
 *
 * The other headers are non-standard, but widely used
 * by popular reverse proxies (like Apache mod_proxy or Amazon EC2).
 */
protected static $trustedHeaders = array(
    self::HEADER_FORWARDED => 'FORWARDED',
    self::HEADER_CLIENT_IP => 'X_FORWARDED_FOR',
    self::HEADER_CLIENT_HOST => 'X_FORWARDED_HOST',
    self::HEADER_CLIENT_PROTO => 'X_FORWARDED_PROTO',
    self::HEADER_CLIENT_PORT => 'X_FORWARDED_PORT',
);

/**
 * Returns the client IP addresses.
 *
 * In the returned array the most trusted IP address is first, and the
 * least trusted one last. The "real" client IP address is the last one,
 * but this is also the least trusted one. Trusted proxies are stripped.
 *
 * Use this method carefully; you should use getClientIp() instead.
 *
 * @return array The client IP addresses
 *
 * @see getClientIp()
 */
public function getClientIps()
{
    $clientIps = array();
    $ip = $this->server->get('REMOTE_ADDR');
    if (!$this->isFromTrustedProxy()) {
        return array($ip);
    }
    if (self::$trustedHeaders[self::HEADER_FORWARDED] && $this->headers->has(self::$trustedHeaders[self::HEADER_FORWARDED])) {
        $forwardedHeader = $this->headers->get(self::$trustedHeaders[self::HEADER_FORWARDED]);
        preg_match_all('{(for)=("?\[?)([a-z0-9\.:_\-/]*)}', $forwardedHeader, $matches);
        $clientIps = $matches[3];
    } elseif (self::$trustedHeaders[self::HEADER_CLIENT_IP] && $this->headers->has(self::$trustedHeaders[self::HEADER_CLIENT_IP])) {
        $clientIps = array_map('trim', explode(',', $this->headers->get(self::$trustedHeaders[self::HEADER_CLIENT_IP])));
    }
    $clientIps[] = $ip; // Complete the IP chain with the IP the request actually came from
    $firstTrustedIp = null;
    foreach ($clientIps as $key => $clientIp) {
        // Remove port (unfortunately, it does happen)
        if (preg_match('{((?:\d+\.){3}\d+)\:\d+}', $clientIp, $match)) {
            $clientIps[$key] = $clientIp = $match[1];
        }
        if (!filter_var($clientIp, FILTER_VALIDATE_IP)) {
            unset($clientIps[$key]);
        }
        if (IpUtils::checkIp($clientIp, self::$trustedProxies)) {
            unset($clientIps[$key]);
            // Fallback to this when the client IP falls into the range of trusted proxies
            if (null ===  $firstTrustedIp) {
                $firstTrustedIp = $clientIp;
            }
        }
    }
    // Now the IP chain contains only untrusted proxies and the client IP
    return $clientIps ? array_reverse($clientIps) : array($firstTrustedIp);
}

虽然这篇文章很老了，但这个话题仍然值得关注。所以我在我的项目中使用了另一个解决方案。我在这里找到了其他的解决方案，要么不完整，要么太复杂，难以理解。

if (! function_exists('get_visitor_IP'))
{
    /**
     * Get the real IP address from visitors proxy. e.g. Cloudflare
     *
     * @return string IP
     */
    function get_visitor_IP()
    {
        // Get real visitor IP behind CloudFlare network
        if (isset($_SERVER["HTTP_CF_CONNECTING_IP"])) {
            $_SERVER['REMOTE_ADDR'] = $_SERVER["HTTP_CF_CONNECTING_IP"];
            $_SERVER['HTTP_CLIENT_IP'] = $_SERVER["HTTP_CF_CONNECTING_IP"];
        }

        // Sometimes the `HTTP_CLIENT_IP` can be used by proxy servers
        $ip = @$_SERVER['HTTP_CLIENT_IP'];
        if (filter_var($ip, FILTER_VALIDATE_IP)) {
           return $ip;
        }

        // Sometimes the `HTTP_X_FORWARDED_FOR` can contain more than IPs 
        $forward_ips = @$_SERVER['HTTP_X_FORWARDED_FOR'];
        if ($forward_ips) {
            $all_ips = explode(',', $forward_ips);

            foreach ($all_ips as $ip) {
                if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE)){
                    return $ip;
                }
            }
        }

        return $_SERVER['REMOTE_ADDR'];
    }
}

你已经回答了你自己的问题!：）

function getRealIpAddr() {
    if(!empty($_SERVER['HTTP_CLIENT_IP']))   //Check IP address from shared Internet
    {
        $IPaddress = $_SERVER['HTTP_CLIENT_IP'];
    }
    elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR']))   //To check IP address is passed from the proxy
    {
        $IPaddress = $_SERVER['HTTP_X_FORWARDED_FOR'];
    }
    else
    {
        $IPaddress = $_SERVER['REMOTE_ADDR'];
    }
    return $IPaddress;
}

源