network programming - How to force ipv6 or ipv4 for HttpWebRequest or WebRequest C#

Question

Coming from node.js I can do this to tell node.js to make the request using ipv6 vs ipv4

var http = require("http");
var options = {
  hostname: "google.com",
  family: 4, // set to 6 for ipv6
};
var req = http.request(options, function(res) {
  .. handle result here ..
});
req.write("");
req.end();

Setting family to 4 forces ipv4, setting it to 6 forces ipv6. Not setting it lets either work.

How can I do the same thing in C# (.NET 3.5)

I can think of one way which is to make a DNS request myself myself for the A or AAAA records, make a direct IP request and set the host: header. Is there a better way?

Answer 1

You can use ServicePoint.BindIPEndPointDelegate.

var req = HttpWebRequest.Create(url) as HttpWebRequest;

req.ServicePoint.BindIPEndPointDelegate = (servicePoint, remoteEndPoint, retryCount) =>
{
    if (remoteEndPoint.AddressFamily == System.Net.Sockets.AddressFamily.InterNetworkV6)
    {
        return new IPEndPoint(IPAddress.IPv6Any, 0);
    }

    throw new InvalidOperationException("no IPv6 address");
};