private void DnsResolve (string host, Action<IPAddress> callback)
		{
			IPAddress addr;
			if (!IPAddress.TryParse (host, out addr)) {
				Dns.BeginGetHostEntry (host, (a) => {
					Enqueue (delegate {
						try {
							IPHostEntry ep = Dns.EndGetHostEntry (a);
							callback (ep.AddressList[0]);
						} catch {
						}
					});
				}, null);
			} else {
				callback (addr);
			}
		}