Bug 11391 - UNHANDLED EXCEPTION: System.Net.Sockets.SocketException: No such host is known
Summary: UNHANDLED EXCEPTION: System.Net.Sockets.SocketException: No such host is known
Alias: None
Product: Android
Classification: Xamarin
Component: BCL Class Libraries ()
Version: 4.6.x
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2013-03-25 11:06 UTC by Wayne Phipps
Modified: 2013-03-27 07:46 UTC (History)
3 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Wayne Phipps 2013-03-25 11:06:46 UTC
Description of Problem:
Using Xamarin Studio 4.0.3 (build 13) on Windows 7 with Build set to Release:
     "UNHANDLED EXCEPTION: System.Net.Sockets.SocketException: No such host is known"
This only occurs when build is set to Release, Debug runs without error?

Steps to reproduce the problem:
1. Take the following code as example:
	public class Activity1 : Activity

		protected override void OnCreate (Bundle bundle)
			base.OnCreate (bundle);

			// Set our view from the "main" layout resource
			SetContentView (Resource.Layout.Main);

			// Get our button from the layout resource,
			// and attach an event to it
			Button button = FindViewById<Button> (Resource.Id.myButton);
			button.Click += delegate {
				button.Text = IPAddress();

		public string IPAddress()
			string hostName = System.Net.Dns.GetHostName();
			System.Net.IPHostEntry hostInfo = System.Net.Dns.GetHostEntry(hostName);
			return hostInfo.AddressList[0].ToString();

Set Build action to Release and Run

Actual Results:
UNHANDLED EXCEPTION: System.Net.Sockets.SocketException No such host is known

Expected Results:
Runs without error in Debug. Consistent results between Debug and Release

How often does this happen? 
All the time

Additional Information:
Comment 1 Wayne Phipps 2013-03-27 07:46:10 UTC
This was answered and resvolved by Jonathan Prior here: http://forums.xamarin.com/discussion/comment/9064#Comment_9064

Your app is missing the INTERNET permission. This is added by default to Debug projects but not Release projects, and is required in order to access network resources.