System.Net.CookieContainer.IsLocal C# (CSharp) Method

        internal bool IsLocal(string host) {

            int dot = host.IndexOf('.');
            if (dot == -1) {
                // No choice but to treat it as a host on the local domain
                // This also covers 'localhost' and 'loopback'
                return true;
            }

            // quick test for usual case
            if (host == "127.0.0.1")
            {
                return true;
            }

            // test domain membership
            if (string.Compare(m_fqdnMyDomain, 0, host, dot, m_fqdnMyDomain.Length, StringComparison.OrdinalIgnoreCase ) == 0)
            {
                return true;
            }

            // test for "127.###.###.###" without using regex
            string[] ipParts = host.Split('.');
            if (ipParts != null && ipParts.Length == 4 && ipParts[0] == "127")
            {
                int i;
                for (i = 1; i < 4; i++)
                {
                    switch (ipParts[i].Length)
                    {
                        case 3:
                            if (ipParts[i][2] < '0' || ipParts[i][2] > '9')
                            {
                                break;
                            }
                            goto case 2;

                        case 2:
                            if (ipParts[i][1] < '0' || ipParts[i][1] > '9')
                            {
                                break;
                            }
                            goto case 1;

                        case 1:
                            if (ipParts[i][0] < '0' || ipParts[i][0] > '9')
                            {
                                break;
                            }
                            continue;
                    }
                    break;
                }
                if (i == 4)
                {
                    return true;
                }
            }

            return false;
        }