Bug 41782 - [Cycle 7] "System.Net.WebException: Error: NameResolutionFailure" when attempting web requests with certain raw IP addresses
Summary: [Cycle 7] "System.Net.WebException: Error: NameResolutionFailure" when attemp...
Alias: None
Product: Class Libraries
Classification: Mono
Component: System (show other bugs)
Version: 4.4.0 (C7)
Hardware: PC Mac OS
: High major
Target Milestone: (C7SR0)
Assignee: Marek Safar
: 41571 41699 41876 41938 41985 (view as bug list)
Depends on: 41571
Blocks: 42864
  Show dependency tree
Reported: 2016-06-14 02:19 UTC by Brendan Zagaeski (Xamarin Team, assistant)
Modified: 2016-09-12 15:36 UTC (History)
16 users (show)

See Also:
Tags: BZRC7S1_C6SR4S1, DefectEscapeReview_Done
Is this bug a regression?: Yes
Last known good build: Mono 4.2.4 (71b88f3)


Description Brendan Zagaeski (Xamarin Team, assistant) 2016-06-14 02:19:00 UTC
[Cycle 7] "System.Net.WebException: Error: NameResolutionFailure" when attempting web requests with certain raw IP addresses

This is a public bug to track the status of non-public Bug 41571.

## Regression status: regression in Cycle 7

BAD:  Mono 4.4.0 (5995f74)
GOOD: Mono 4.2.4 (71b88f3)

## Steps to replicate

1. Replace the IP address in the following 2 lines with a "bad" IP address that shows the problem:

var request = WebRequest.CreateHttp ("");
request.GetResponse ();

2. Run the request.

## Results

The request fails:

> System.Net.WebException: Error: NameResolutionFailure
>   at System.Net.HttpWebRequest.EndGetResponse (IAsyncResult asyncResult) <0x27cf0d0 + 0x00187> in <filename unknown>:0 
>   at System.Net.HttpWebRequest.GetResponse () <0x27c74c0 + 0x0004c> in <filename unknown>:0 
>   at ConsoleApp1.MainClass.Main (System.String[] args) <0x6eeec8 + 0x0001b> in <filename unknown>:0 

If you set the IDE to break whenever a System.Exception is thrown, you can get a bit more interesting stack trace for a "System.Net.Sockets.SocketException":

>   at System.Net.Dns.Error_11001(string hostName) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/System/System.Net/Dns.cs:292
>   at System.Net.Dns.GetHostByAddressFromString(string address, bool parse) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/System/System.Net/Dns.cs:361
>   at System.Net.Dns.GetHostEntry(System.Net.IPAddress address) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/System/System.Net/Dns.cs:388
>   at System.Net.Dns.GetHostEntry(string hostNameOrAddress) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/System/System.Net/Dns.cs:378
>   at System.Net.ServicePoint.get_HostEntry() in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/System/System.Net/ServicePoint.cs:352
>   at System.Net.WebConnection.Connect(System.Net.HttpWebRequest request) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/System/System.Net/WebConnection.cs:152
>   at System.Net.WebConnection.InitConnection(System.Net.HttpWebRequest state) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/System/System.Net/WebConnection.cs:703
>   at System.Net.WebConnection.AnonymousMethod__0(System.Net.HttpWebRequest state) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/System/System.Net/WebConnection.cs:106
>   at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(System.Threading.QueueUserWorkItemCallback state) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/external/referencesource/mscorlib/system/threading/threadpool.cs:1307
>   at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Threading.QueueUserWorkItemCallback state, bool preserveSyncCtx) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/external/referencesource/mscorlib/system/threading/executioncontext.cs:957
>   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Threading.QueueUserWorkItemCallback state, bool preserveSyncCtx) in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/external/referencesource/mscorlib/system/threading/executioncontext.cs:904
>   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem() in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/external/referencesource/mscorlib/system/threading/threadpool.cs:1284
>   at System.Threading.ThreadPoolWorkQueue.Dispatch() in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/external/referencesource/mscorlib/system/threading/threadpool.cs:857
>   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback() in /private/tmp/source-mono-4.4.0-c7-baseline/bockbuild-mono-4.4.0-c7-baseline/profiles/mono-mac-xamarin/build-root/mono-x86/external/referencesource/mscorlib/system/threading/threadpool.cs:1212
Comment 2 Brendan Zagaeski (Xamarin Team, assistant) 2016-06-14 02:31:41 UTC
## Additional information

- I attempted to replicate the problem without depending on a customer's endpoint.  I set a VM to have exactly the same "bad" IP address and ran an HTTP server on it.  Unfortunately, that setup worked _without_ error.  So the problem might require some other detail of server configuration or network routing that was not present in that simpler local setup.

- I also tested another 20 common IP addresses for various websites, but so far I haven't found any additional addresses that hit this issue.  I don't have any guesses about what makes certain IP addresses "special" in the context of this bug.
Comment 3 Brendan Zagaeski (Xamarin Team, assistant) 2016-06-14 02:32:33 UTC
*** Bug 41699 has been marked as a duplicate of this bug. ***
Comment 4 Brendan Zagaeski (Xamarin Team, assistant) 2016-06-14 02:41:49 UTC
## Possible workarounds

- Use domain names rather than IP addresses for the web requests.

- If possible, try an alternate IP address for the same resource.  With a little bit of luck, the problem might not affect the second IP address.

## Downgrading

If needed, you can also downgrade temporarily as described under "Updating and downgrading" on the Cycle 7 forum announcement:

Comment 7 Brendan Zagaeski (Xamarin Team, assistant) 2016-06-15 16:18:13 UTC
For thorough cross-referencing, I'll record that this issue is now included in the known issues section of the releases notes for Xamarin.iOS, Xamarin.Android, and Xamarin.Mac.:

- https://developer.xamarin.com/releases/ios/xamarin.ios_9/xamarin.ios_9.8/#Known_Issues

- https://developer.xamarin.com/releases/android/xamarin.android_6/xamarin.android_6.1/#Known_Issues

- https://developer.xamarin.com/releases/mac/xamarin.mac_2/xamarin.mac_2.8/#Releases
Comment 8 Marek Safar 2016-06-16 13:42:31 UTC
*** Bug 41571 has been marked as a duplicate of this bug. ***
Comment 9 Marek Safar 2016-06-16 17:20:41 UTC
Fixed in master and Mono 4.5.

A fix for Mono 4.4 is waiting in service release queue.
Comment 10 Marek Safar 2016-06-16 19:18:43 UTC
*** Bug 41876 has been marked as a duplicate of this bug. ***
Comment 11 Mohit Kheterpal 2016-06-17 14:42:44 UTC
To verify this issue, I am using the sample provided in its duplicate bug 41571.

Now, I am not getting error mentioned in bug description, But I am getting following error : 

Error - There was an error on processing web request: Status code 405(MethodNotAllowed): Method Not Allowed

Not sure, is this expected behaviour for the sample attached in Bug 41571 or is this different issue.

Could you please confirm ?

Comment 12 Brendan Zagaeski (Xamarin Team, assistant) 2016-06-17 15:55:38 UTC
Yes, that is the expected behavior as described in non-public Bug 41571, Comment 2.  I will mark this bug as "verified" accordingly.  Thanks for the test!
Comment 13 Brendan Zagaeski (Xamarin Team, assistant) 2016-06-17 17:01:03 UTC
*** Bug 41938 has been marked as a duplicate of this bug. ***
Comment 14 Marek Safar 2016-06-20 07:24:39 UTC
*** Bug 41985 has been marked as a duplicate of this bug. ***
Comment 15 Ace Olszowka 2016-07-27 20:13:11 UTC
We're still seeing this as of Xamarin.Android 6.1.1 (7bd2aac)/Xamarin 4.1.13 (34a92cd); however it only appears on the SECOND request. I'm opening a new private case with a repo'ing project.
Comment 16 Jean-Baptiste 2016-07-28 15:29:55 UTC
we also have that issue. 
file : https://github.com/mono/mono/blob/e233950c6e237843c1658d386e3347c7b78f5c37/mcs/class/System/System.Net/ServicePoint.cs

line 363 -> the if must be TRUE is this is a IP address in all cases
Comment 17 Brendan Zagaeski (Xamarin Team, assistant) 2016-07-28 15:32:48 UTC
@Jean-Baptiste, that issue has been filed in its own follow-up bug linked to this one under the "Blocks" field: Bug 42864.

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