Test failure: GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok times out on macOS (runtime-extra-platforms) #132750

Test failure

System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok is failing intermittently on macOS (OSX.15.Amd64.Open, OSX.26.Arm64.Open) in the runtime-extra-platforms pipeline.

Error message

System.TimeoutException : The operation has timed out.

Frequency

8 builds on main over the past 14 days (plus a few PR runs), exclusively on macOS queues. Ongoing since 2026-08-12.

Analysis

This is the macOS name-resolution flakiness long tracked by the umbrella issue #1488. The sibling GetHostEntry* tests already opt out of macOS via the GetHostEntryWorks gate, which is annotated with that issue:

src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs

public static bool GetHostEntryWorks =
    // [ActiveIssue("https://github.com/dotnet/runtime/issues/27622")]
    PlatformDetection.IsNotArmNorArm64Process &&
    // [ActiveIssue("https://github.com/dotnet/runtime/issues/1488", TestPlatforms.OSX)]
    !PlatformDetection.IsOSX &&
    ...

However, Dns_GetHostEntryAsync_IPAddress_Ok is not covered by that gate — it only requires multithreading:

[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsMultithreadingSupported))]
public async Task Dns_GetHostEntryAsync_IPAddress_Ok()
{
    IPAddress localIPAddress = await TestSettings.GetLocalIPAddress();
    await TestGetHostEntryAsync(() => Dns.GetHostEntryAsync(localIPAddress));
}

So the reverse lookup of the local IP address (Dns.GetHostEntryAsync(localIPAddress)) intermittently times out on the macOS CI resolver, exactly the flakiness #1488 describes for the other tests. Filing a dedicated Known Build Error so Build Analysis can auto-match this specific failure (the umbrella #1488 has no known-issue JSON blob).

Suggested fix

Gate this test on macOS the same way as its siblings — add !PlatformDetection.IsOSX (referencing #1488) to the condition, or move it behind the existing GetHostEntryWorks check.

Sample console log

https://helixr1107v0xdeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-heads-main-51264a0b9e1b49bb9f/System.Net.NameResolution.Functional.Tests/2/console.58c2e797.log?helixlogtype=result

Known issue error message

Fill the error message using known issues.

{
  "ErrorPattern": "System\\.Net\\.NameResolution\\.Tests\\.GetHostEntryTest\\.Dns_GetHostEntryAsync_IPAddress_Ok",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1564198
Error message validated: [System\.Net\.NameResolution\.Tests\.GetHostEntryTest\.Dns_GetHostEntryAsync_IPAddress_Ok]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 8/25/2026 2:38:20 PM UTC

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