C#/.NET: FInd out whether a server exists, Query DNS for SVC records.

Question

Writing a cleint/Server tool I am tasked trying to find a server to connect to. I would love to make things as easy as possible for the user. As such, my idea is to:

• CHeck whether specific servers (coded by name) exist (like "mail.xxx" for a mail server, for example - my exampüle is not a mail server;)
• Query otherwise for DNS SVC records, allowing the admin to configure a server location for a specific serivce (that the client connects to).

The result is that the user may have to enter only a domain name, possibly even not even that (using the registered standard domain of the computer in a LAN environment).

Anyone ideas how:

• To find out whether a server exists and answers (i.e. is online) in the fastest way? TCP can take a long time if the server is not there. A UDP style ping sounds like a good idea to me. PING itself may be unavailable.
• Anyonw knows how to ask from withint .NET best for a SVC record in a specific (the default) domain?

Answer 1

You can use ping from .NET but it needs the ip address of the server.

From here:

internal bool PingServer()
        {
            bool netOK = false;
            // 164.110.12.144 is current server address for server: nwhqsesan02

            byte[] AddrBytes = new byte[] { 164, 110, 12, 144 }; // byte array for server address.
            using (System.Net.NetworkInformation.Ping png = new System.Net.NetworkInformation.Ping())

            {
                System.Net.IPAddress addr;
                // Sending ping to a numeric byte address has the best change of 
                // never causing en exception, whether network connected or not.
                addr = new System.Net.IPAddress(AddrBytes);
                try
                {
                    netOK = (png.Send(addr, 1500, new byte[] { 0, 1, 2, 3 }).Status == IPStatus.Success);
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString()); 
                    netOK = false;
                }
                return netOK;
            }
        }

EDIT: How about this:

bool ConnectionExists()
{
try
{
System.Net.Sockets.TcpClient clnt=new System.Net.Sockets.TcpClient("www.google.com",80);
clnt.Close();
return true;
}
catch(System.Exception ex)
{
return false;

} }

Answer 2

The best way to test if a service exists and is alive is probably using the native protocol of that service. Otherwise I would go with ping (ICMP ECHO).

As for looking up the SRV-record (I assume you mean "SRV" sinces there is no "SVC" type), you could use the "DNS Client Library for .NET" (http://www.simpledns.com/dns-client-lib.aspx) - for example:

var Response = JHSoftware.DnsClient.Lookup("_ftp._tcp.xyz.com", 
                                       JHSoftware.DnsClient.RecordType.SRV);