string errorOctet;

public bool InvalidOctet(string ip)
        {
            ipErrorNum = 0;

            string[] subOctets = new string[4];
            string[] postContent = new string[4];
            int[] octetCounts = new int[4];
            int[] subOctetNums = new int[4];

            postContent[0] = ip;
            bool addOperation = false;
            int[] iterator = new int[2];

            try
            {

                for (int i = 0; i < 4; i++)
                {
                    if (addOperation == true)
                    {
                        postContent[i] = postContent[i - 1].Replace(subOctets[i - 1], "");

                    }
                    if (iterator[0] == 3)
                    {

                        subOctets[i] = postContent[i];
                        break;
                    }

                    octetCounts[i] = postContent[i].IndexOf('.');
                    subOctets[i] = postContent[i].Substring(0, octetCounts[i] + 1);

                    iterator[0]++;
                    addOperation = true;
                }

                for (int i = 0; i < subOctets.Length; i++)
                {

                    if (iterator[1] < 3)
                    {
                        subOctets[i] = subOctets[i].Replace(".", "");
                    }
                    subOctetNums[i] = Convert.ToInt32(subOctets[i]);
                    if (subOctetNums[i] > 255 || subOctetNums[i] < 0)
                    {
                        ipErrorNum = invalidOctet;
                        errorOctet = "octet index = " + (i + 1) + "  " + "octet number = " + subOctetNums[i].ToString();
                        MessageBox.Show("Invalid IP!");
                        return true;
                    }
                    iterator[1]++;
                }

                MessageBox.Show(subOctets[0] + " | " + subOctets[1] + " | " + subOctets[2] + " | " + subOctets[3]);

                return false;
            }
            catch (Exception ex) { }
            return false;
        }