Android socket tests failing with IPv6 connectivity issues

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Description

Multiple socket tests are failing on Android Helix machines in the runtime-extra-platforms pipeline. The failures appear to be infrastructure/environment-related rather than code regressions.

Failing Tests

1. System.Net.Sockets.Tests.DualModeConnectToDnsEndPoint.DualModeConnect_DnsEndPointToHost_Helper(listenOn: ::1, dualModeServer: False)

   • Error: SocketException: Connection refused [::ffff:10.64.33.238]:34855

2. System.Net.Sockets.Tests.DualModeConnectAsync.DualModeConnectAsync_DnsEndPointToHost_Helper(listenOn: ::1, dualModeServer: False)

   • Error: SocketException: Connection refused

3. System.Net.Sockets.Tests.SocketBlockingModeTransitionTests.ConnectAsync_WithBuffer_Succeeds

   • Error: Assert.False() Failure (expected blocking mode behavior not met)

4. System.Net.Sockets.Tests.SocketAsyncEventArgsTest.Connect_Parallel_FailsOver(preferIPv6: True)

   • Error: Assert.NotNull() Failure: Value is null

Analysis

These failures appear to be infrastructure issues:

• IPv6 connectivity problems: Tests listening on ::1 (IPv6 loopback) fail with "Connection refused", suggesting IPv6 is not properly configured on the Android emulators
• Dual-stack socket behavior: Tests expecting dual-mode sockets to work correctly are failing, consistent with IPv6 configuration issues
• Intermittent blocking mode transitions: Suggests timing or thread synchronization issues in the test environment

Failure Details

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1396313

Job: android-arm64 Release AllSubsets_Mono

Helix Work Item:

• Job ID: 93091357-214b-436d-a5c4-a31ee456a876
• Work Item: System.Net.Sockets.Tests
• Console log: https://helix.dot.net/api/2019-06-17/jobs/93091357-214b-436d-a5c4-a31ee456a876/workitems/System.Net.Sockets.Tests/console

Log excerpt:

04-25 00:09:05.266  DOTNET  : [FAIL] System.Net.Sockets.Tests.DualModeConnectToDnsEndPoint.DualModeConnect_DnsEndPointToHost_Helper(listenOn: ::1, dualModeServer: False)
04-25 00:09:05.266  DOTNET  : System.Net.Sockets.SocketException : Connection refused [::ffff:10.64.33.238]:34855

Recommendations

1. Skip IPv6-specific tests on Android if IPv6 is not reliably available on Helix machines
2. Investigate Android emulator IPv6 configuration in Helix provisioning
3. Consider adding ActiveIssue attributes to the affected tests to track the infrastructure limitation

Related

• Similar iOS socket issues may exist (needs verification)

Note

🔒 Integrity filter blocked 1 item

The following item were blocked because they don't meet the GitHub integrity level.

• #126805 search_pull_requests: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".

To allow these resources, lower min-integrity in your GitHub frontmatter:

tools:
  github:
    min-integrity: approved  # merged | approved | unapproved | none

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Latest Occurrence

The socket failures continue to reproduce in build #1396313 (2026-04-25).

Android Helix Job

• Job ID: 93091357-214b-436d-a5c4-a31ee456a876
• Console log: https://helix.dot.net/api/2019-06-17/jobs/93091357-214b-436d-a5c4-a31ee456a876/workitems/System.Net.Sockets.Tests/console

Additional affected platforms: iossimulator-arm64, iossimulator-x64, tvos-arm64, maccatalyst-arm64, maccatalyst-x64 (all Mono and CoreCLR).

Additional Failure: NameResolution Tests

The System.Net.NameResolution.Functional.Tests workitem also failed with multiple tests failing on localhost resolution:

Sample failure:

System.Net.NameResolution.Tests.GetHostEntryTest.DnsGetHostEntry_LocalHost_ReturnsFqdnAndLoopbackIPs(mode: 0)
Assert.All() Failure: 5 out of 6 items in the collection did not pass.
Error: Not a loopback address: 10.64.32.211

Tests affected:

• DnsGetHostEntry_LocalHost_ReturnsFqdnAndLoopbackIPs
• DnsGetHostEntry_LocalhostSubdomain_ReturnsLoopback (multiple variants)
• DnsGetHostAddresses_LocalhostSubdomain_ReturnsLoopback (multiple variants)

Root cause: Android DNS resolution for localhost returns the machine's network IP (10.64.32.211) instead of loopback addresses (127.0.0.1 / ::1), causing assertions to fail.

Recommendation: Skip these tests on Android with [SkipOnPlatform(TestPlatforms.Android, "Android DNS does not resolve localhost to loopback addresses")].

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