判斷IP是否為內部IP

 public static class IPAddressExtensions

    {

        /// <summary>

        /// Returns true if the IP address is in a private range.<br/>

        /// IPv4: Loopback, link local ("169.254.x.x"), class A ("10.x.x.x"), class B ("172.16.x.x" to "172.31.x.x") and class C ("192.168.x.x").<br/>

        /// IPv6: Loopback, link local, site local, unique local and private IPv4 mapped to IPv6.<br/>

        /// </summary>

        /// <param name="ip">The IP address.</param>

        /// <returns>True if the IP address was in a private range.</returns>

        /// <example><code>bool isPrivate = IPAddress.Parse("127.0.0.1").IsPrivate();</code></example>

        public static bool IsPrivate(this System.Net.IPAddress ip)

        {

            // Map back to IPv4 if mapped to IPv6, for example "::ffff:1.2.3.4" to "1.2.3.4".

            if (ip.IsIPv4MappedToIPv6)

                ip = ip.MapToIPv4();

            // Checks loopback ranges for both IPv4 and IPv6.

            if (System.Net.IPAddress.IsLoopback(ip)) return true;

            // IPv4

            if (ip.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)

                return IsPrivateIPv4(ip.GetAddressBytes());

            // IPv6

            if (ip.AddressFamily == System.Net.Sockets.AddressFamily.InterNetworkV6)

            {

                return ip.IsIPv6LinkLocal ||

#if NET6_0

                       ip.IsIPv6UniqueLocal ||

#endif

                       ip.IsIPv6SiteLocal;

            }

            throw new NotSupportedException(

                    $"IP address family {ip.AddressFamily} is not supported, expected only IPv4 (InterNetwork) or IPv6 (InterNetworkV6).");

        }

        private static bool IsPrivateIPv4(byte[] ipv4Bytes)

        {

            // Link local (no IP assigned by DHCP): 169.254.0.0 to 169.254.255.255 (169.254.0.0/16)

            bool IsLinkLocal() => ipv4Bytes[0] == 169 && ipv4Bytes[1] == 254;

            // Class A private range: 10.0.0.0 – 10.255.255.255 (10.0.0.0/8)

            bool IsClassA() => ipv4Bytes[0] == 10;

            // Class B private range: 172.16.0.0 – 172.31.255.255 (172.16.0.0/12)

            bool IsClassB() => ipv4Bytes[0] == 172 && ipv4Bytes[1] >= 16 && ipv4Bytes[1] <= 31;

            // Class C private range: 192.168.0.0 – 192.168.255.255 (192.168.0.0/16)

            bool IsClassC() => ipv4Bytes[0] == 192 && ipv4Bytes[1] == 168;

            return IsLinkLocal() || IsClassA() || IsClassC() || IsClassB();

        }

    }

舉例用法 : 檢查函數呼叫者是否來自內部IP

public static string xxx() {

var clientIP = System.Net.IPAddress.Parse(HttpContext.Current.Request.UserHostAddress);

if (!clientIP.IsPrivate()) throw new Exception("非法呼叫!!");

}

來源