dns: fix Windows SRV ECONNREFUSED regression by correcting c-ares fallback detection

[NotVivek12]

dns: fix Windows SRV ECONNREFUSED regression by correcting c-ares fallback detection

Summary

This PR fixes a regression introduced in Node.js v24.13.0 on Windows where DNS SRV lookups (commonly used by MongoDB connection strings) fail with ECONNREFUSED.

The issue stems from a change in c-ares behavior where the fallback resolver (loopback) is reported with port 53 rather than port 0. The existing Node.js glue layer strictly expected port 0 to identify a fallback scenario. Consequently, Node.js failed to detect the fallback, attempting to query a non-listening local stub resolver at 127.0.0.1:53 or [::1]:53.

Changes

1. **Updated ChannelWrap::EnsureServers**: Modified logic to treat any single loopback server (IPv4 127.0.0.1 or IPv6 ::1) as a fallback configuration, regardless of the port number reported by c-ares.
2. Proactive Validation: Added a call to EnsureServers() immediately before dispatching queries in the Query template to ensure the channel is correctly initialized before use.

Regression Details

• Affected Version: Node.js v24.13.0
• Platform: Windows 11 / Server
• Error: Error: querySrv ECONNREFUSED
• Last Known Good: v24.11.1

Reproduction

This issue is 100% reproducible on Windows with Node v24.13.0 using the following script (mimicking a standard Mongoose connection):

const express = require("express");
const mongoose = require("mongoose");
const app = express();

const connectDB = async () => {
  try {
    // Replace with a valid SRV URI
    const conn = await mongoose.connect("mongodb+srv://<user>:<pass>@cluster0.example.mongodb.net/db");
    console.log(`MongoDB Connected: ${conn.connection.host}`);
  } catch (error) {
    console.error('MongoDB connection failed:', error.message);
    process.exit(1);
  }
};
connectDB();

app.listen(3300, () => {
  console.log("mongodb connected at port 3300");
});

Output on v24.13.0:
Error: querySrv ECONNREFUSED _mongodb._tcp.cluster0.example.mongodb.net

Manual Verification

1. Built Node.js from source on Windows (VS 2022 Build Tools).
2. Ran the reproduction script above; connection succeeds.
3. Verified dns.getServers() no longer returns a single loopback address when the system resolver is active.

Risks

Low.

• The logic only activates when c-ares discovers a single loopback server and the user has not manually called setServers().
• If setServers() is called, is_servers_default_ becomes false, skipping this check entirely.
• The logic is platform-agnostic but primarily resolves the specific behavior observed on Windows.

Workaround for users

Users on v24.13.0 can temporarily work around this by forcing DNS servers before connection:

require('dns').setServers(['8.8.8.8', '1.1.1.1']);

---

Checklist

• Fixes regression in dns / c-ares
• Tested on Windows
• Tests added/verified (Manual verification performed)

[nodejs-github-bot]

Review requested:

• @nodejs/net

[Ethan-Arrowood]

Do you think you could add a tests so we don't see this regression again in the future? Thanks!

[NotVivek12]

Do you think you could add a tests so we don't see this regression again in the future? Thanks!

Absolutely, happy to add a test. Did you have a specific scenario in mind, or should I just cover the case from the original bug report?

[NotVivek12]

Sure, I've added regression tests for this! Created two test files:

test-dns-resolvesrv.js- basic SRV resolution tests
test-dns-resolvesrv-econnrefused.js- specifically tests the ECONNREFUSED regression with MongoDB Atlas-style SRV lookups
Also added SRV record support to dns.js so we can mock SRV responses.

[addaleax]

Thank you @NotVivek12! This largely looks good, just have two questions here

[codecov]

Codecov Report

❌ Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.75%. Comparing base (f77a709) to head (358a6f9).
⚠️ Report is 189 commits behind head on main.

Files with missing lines	Patch %	Lines
src/cares_wrap.cc	11.11%	8 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #61453   +/-   ##
=======================================
  Coverage   89.74%   89.75%           
=======================================
  Files         674      674           
  Lines      204360   204365    +5     
  Branches    39265    39266    +1     
=======================================
+ Hits       183412   183424   +12     
+ Misses      13251    13241   -10     
- Partials     7697     7700    +3     

Files with missing lines	Coverage Δ
src/cares_wrap.cc	61.73% <11.11%> (+1.42%)	⬆️

... and 23 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[addaleax]

@NotVivek12 Can you look at the linter failures? Looks like there's some failing tasks

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/71106/

[NotVivek12]

@NotVivek12 Can you look at the linter failures? Looks like there's some failing tasks

Hello, ive made the changes trying to resolve these errors. Hope it works.

[addaleax]

Kicked off CI to see how well this does, but we'll probably need to remove package-lock.json again before this can be merged

[github-actions]

Failed to start CI

   ⚠  Commits were pushed since the last approving review:
   ⚠  - fix fix Windows SRV ECONNREFUSED regression
   ⚠  - Merge branch 'main' of https://github.com/NotVivek12/node
   ⚠  - Merge branch 'nodejs:main' into main
   ⚠  - add regression tests
   ⚠  - remove unintentional file
   ⚠  - Merge branch 'nodejs:main' into main
   ⚠  - Merge branch 'main' of https://github.com/NotVivek12/node
   ⚠  - fix CI/CD errors
   ⚠  - Merge branch 'nodejs:main' into main
   ⚠  - Merge branch 'main' of https://github.com/NotVivek12/node
   ✘  Refusing to run CI on potentially unsafe PR

https://github.com/nodejs/node/actions/runs/21514988012

[NotVivek12]

Hi @addaleax i tried looking for what caused these tests to fail and couldnt figure out what the exact issues were, could you please help me figure out what these issues were caused by, so that i could come up with the fix for these.

[addaleax]

Sure, let's do another one and see if/where it fails

[nachocodoner]

Is this fix cherry picked for Node 22.x series? I have got reports from users on Node 22 happening this problem.

[omni-htg]

Hello team! Would this be introduced in the LTS version as well?
I noticed that, while the tags were added for it, the latest patch update (24.13.1, 2 days ago, Feb 10) did not include this (or at least it's not mentioned as part of the changelog), and would love to know what the expected timeline would be.

On a separate note, this is also unfortunately affecting mongodb-js/mongosh indirectly on Windows, I believe.

Thanks team!

[NotVivek12]

Landed in 8c32389 (adjusted commit message during merge to make it adhere to our linter rules)

Thank You so much for doing that for me.

[jasonradford115-ui]

Help

[hufftheweevil]

This bug appears to still exist in 24.14.0 for Windows
Using nvm, I switch to 24.11.1 and it works fine. But in 24.14.0, the querySrv ECONNREFUSED occurs.

[bfletcher-dijones]

@NotVivek12 My understanding is that this regression was caused by c-ares/c-ares#1034 which caused c-ares/c-ares#1056. Does that specific c-ares change match up with the behaviour change you described: 'change in c-ares behavior where the fallback resolver (loopback) is reported with port 53'?

If so, then I believe this c-ares regression landed in Node when Node bumped the c-ares dep for a security release in January 2026. This c-ares dep bump shipped in v20.20.0, v22.22.0, v24.13.0, and v25.3.0. That means this PR needs to be shipped into v20, v22, v24, and v25. This PR has landed in v24 and v25 but NOT v20 or v22.

Yes v20 and v22 are in MAINTENANCE not ACTIVE, but this regression was introduced in a security update, so I think it's reasonable to say that the fix for the regression should also ship to v20 and v22.

[febkosq8]

This bug appears to still exist in 24.14.0 for Windows Using nvm, I switch to 24.11.1 and it works fine. But in 24.14.0, the querySrv ECONNREFUSED occurs.

Can confirm I get the same issue when on 24.14.0, but it works fine on 24.11.1

[Alamin-22]

Reproduced on Windows 11 with Node v24.14.0 and v22.22.0. Downgrading to v24.11.1 or v22.13.1 fixed the issue. The error was querySrv ECONNREFUSED when connecting to MongoDB Atlas.

[antoineskt]

Reproduced on Windows 11 with Node v24.14.1 and v24.13.1. Downgrading to v24.11.1 fixed the issue. The error was querySrv ECONNREFUSED when connecting to MongoDB Atlas as well.

[rtritto]

I still have this issue with Node.js versions:

• 24.16.0 (latest LTS)
• 26.2.0 (latest v26)

FYI @marco-ippolito @addaleax

[SyedJunaidAli1]

same issue still going on with

node : 26.3.1
on windows 11