[ci-scan] Test failure: DnsGetHostAddresses_LocalhostSubdomainWithTrailingDot_ReturnsLoopback on android

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Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1413202
Build error leg or test failing: android-arm64 Release AllSubsets_CoreCLR - System.Net.NameResolution.Functional.Tests

Error Message

{
  "ErrorMessage": "[FAIL] System.Net.NameResolution.Tests.GetHostAddressesTest.DnsGetHostAddresses_",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Additional Context

Summary: GetHostAddressesTest.DnsGetHostAddresses_LocalhostSubdomainWithTrailingDot_ReturnsLoopback fails on android-arm64 because DNS resolution of foo.localhost. and bar.test.localhost. returns non-loopback addresses (host network interfaces) instead of loopback.

Failed in (10+):

• runtime-extra-platforms 1413202 (2026-05-08)
• runtime-extra-platforms 1411505 (2026-05-07)
• All 10 checked builds have android-arm64 CoreCLR failing (test is part of the failing work item)

Console Log: android-arm64 Console Log

Failed tests:

runtime-extra-platforms (android-arm64 Release AllSubsets_CoreCLR)
- Windows.11.Amd64.Android.Open
  - System.Net.NameResolution.Tests.GetHostAddressesTest.DnsGetHostAddresses_LocalhostSubdomainWithTrailingDot_ReturnsLoopback(hostName: "foo.localhost.")
  - System.Net.NameResolution.Tests.GetHostAddressesTest.DnsGetHostAddresses_LocalhostSubdomainWithTrailingDot_ReturnsLoopback(hostName: "bar.test.localhost.")

Error Message:

[FAIL] System.Net.NameResolution.Tests.GetHostAddressesTest.DnsGetHostAddresses_LocalhostSubdomainWithTrailingDot_ReturnsLoopback(hostName: "foo.localhost.")
Assert.All() Failure: 7 out of 8 items in the collection did not pass.
     Error: Expected loopback address but got: fe80::2dd7:ff44:eff:c764%30
     Error: Expected loopback address but got: 10.64.33.196

Impact on platforms:

• runtime-extra-platforms + android-arm64 + Windows.11.Amd64.Android.Open + exit code 1

First build it occurred: First seen in build 1396313 (2026-04-25) within the scanned window. 10/10 builds affected. Note: this is the earliest in the scanned window and may not be the true origin.

Recommended action: Android DNS resolution does not treat *.localhost subdomains as loopback per RFC 6761 the same way desktop OSes do. The test assumptions about foo.localhost. resolving to loopback are not valid on Android. The test should be annotated with [ActiveIssue] for Android or the test should skip when PlatformDetection.IsAndroid is true. Area owners: @dotnet/ncl.

Generated by CI Outer-Loop Failure Scanner · ● 26.1M · ◷

[jkotas]

"ErrorMessage": "DnsGetHostAddresses_LocalhostSubdomainWithTrailingDot_ReturnsLoopback",

@kotlarmilos These error matching patterns are not specific enough. This string is going to match even when unrelated test fails and this one passes (names of passing tests are often in the test logs as well).

[kotlarmilos]

I updated this and other issues manually, and based on feedback, created #127961. We might need a few more iterations to get it right. Let me know when/if it starts generating too much noise and I'll reduce the scope to a subset of tests for the additional iterations.