Recipe 13.2 Converting a Hostname to an IP Address

Problem

You have a string representation of a host (such as www.oreilly.com ), and you need to obtain the IP address from this hostname.

Solution

Use the Dns.Resolve method to get the IP addresses. In the following code, a hostname is provided to the Resolve method that returns an IPHostEntry from which a string of addresses can be constructed and returned:

 using System; using System.Net; using System.Text; // ... public static string HostName2IP(string hostname) {     // resolve the hostname into an iphost entry using the dns class     IPHostEntry iphost = System.Net.Dns.Resolve(hostname);     // get all of the possible IP addresses for this hostname     IPAddress[] addresses = iphost.AddressList;     // make a text representation of the list     StringBuilder addressList = new StringBuilder( );     // get each ip address     foreach(IPAddress address in addresses)     {         // append it to the list         addressList.Append("IP Address: ");         addressList.Append(address.ToString( ));         addressList.Append(";");     }     return addressList.ToString( ); } // ... // writes "IP Address: 208.201.239.37;IP Address: 208.201.239.36;" Console.WriteLine(HostName2IP("www.oreilly.com")); 

Discussion

An IPHostEntry can associate multiple IP addresses with a single hostname via the AddressList property. AddressList is an array of IPAddress objects, each of which holds a single IP address. Once the IPHostEntry is resolved, the AddressList can be looped over using foreach to create a string that shows all of the IP addresses for the given hostname.

See Also

See the "DNS Class," "IPHostEntry Class," and "IPAddress" topics in the MSDN documentation.