Check Format of DNS or IP

got it

You should use a regularexpression that checks the input string format. You can find a lot of regularexpression on the web

Softair, Try this. It's not a very effecient way to check the IP or DNS, but until someone else posts a bbetter answer... //At the top of your code add: //using System.Net; string sHost = txtHost.Text.Trim(); //check if string is an IP address try { //make sure at the top of your code you use //using System.Net; IPAddress validIp = IPAddress.Parse(sHost); } //if it's not an IP address, try it as a dns catch { bool validPrefix = false; bool validDns = false; //add as many prefixes as you want string[] dnsPrefixes = new string[]{ "http:\\www.", "www.", "ftp." }; //again, add as many suffixes as needed string[] dnsSuffixes = new string[]{ ".com", ".net", ".gov", ".org", ".mil", ".edu", ".co", ".uk" }; foreach(string prefix in dnsPrefixes) { //the prefix needs to be at the beginning of the address if(sHost.ToLower().IndexOf(prefix) == 0) { validPrefix = true; } } //if we have a valid prefix, check the suffix if(validPrefix == true) { foreach(string suffix in dnsSuffixes) { //the suffix can't be at the beginning if(sHost.ToLower().IndexOf(suffix) >= 3) { validDns = true; } } } //if it isn't a dns, then display your message to enter a host if(validDns != true) { MessageBox.Show("Please enter Host!","Warning",MessageBoxButtons.OK,MessageBoxIcon.Information); txtHost.Focus(); } } I hope this will help you temporarily ;)