[PR #6183] [client] Filter DNS fallback upstreams matching our server IP to prevent loops #27704

New Issue

saavagebueno · 2026-08-05T07:09:07-04:00

saavagebueno commented

2026-08-05 07:09:07 -04:00

Original Pull Request: https://github.com/netbirdio/netbird/pull/6183

State: closed
Merged: Yes

Describe your changes

Skip any captured original nameserver that matches our own DNS listener IP when building the PriorityFallback upstream handler. Without this, hosts whose /etc/resolv.conf happened to list the NetBird tunnel IPcaused the fallback handler to race DNS queries against itself, producing a DNS loop.

Filter s.service.RuntimeIP() out of the fallback upstream list
Bail through clearFallback() if filtering leaves no usable upstreams, so no empty handler gets registered

Issue ticket number and link

#6182

Stack

Checklist

Is it a bug fix
Is a typo/documentation fix
Is a feature enhancement
It is a refactor
Created tests that fail without the change (if possible)

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Documentation

Select exactly one:

I added/updated documentation for this change
Documentation is not needed for this change (explain why)

Internal bug fix in DNS fallback path, no user-facing API or behavior to document.

Docs PR URL (required if "docs added" is checked)

Paste the PR link from https://github.com/netbirdio/docs here:

https://github.com/netbirdio/docs/pull/__

Summary by CodeRabbit

Bug Fixes
- Fixed DNS fallback handling to properly exclude the server's own IP address from the fallback nameserver list, improving DNS resolution reliability in scenarios where fallback servers are needed.

**Original Pull Request:** https://github.com/netbirdio/netbird/pull/6183 **State:** closed **Merged:** Yes --- ## Describe your changes Skip any captured original nameserver that matches our own DNS listener IP when building the PriorityFallback upstream handler. Without this, hosts whose `/etc/resolv.conf` happened to list the NetBird tunnel IPcaused the fallback handler to race DNS queries against itself, producing a DNS loop. - Filter `s.service.RuntimeIP()` out of the fallback upstream list - Bail through `clearFallback()` if filtering leaves no usable upstreams, so no empty handler gets registered ## Issue ticket number and link #6182 ## Stack  ### Checklist - [x] Is it a bug fix - [ ] Is a typo/documentation fix - [ ] Is a feature enhancement - [ ] It is a refactor - [ ] Created tests that fail without the change (if possible) > By submitting this pull request, you confirm that you have read and agree to the terms of the [Contributor License Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md). ## Documentation Select exactly one: - [ ] I added/updated documentation for this change - [x] Documentation is **not needed** for this change (explain why) Internal bug fix in DNS fallback path, no user-facing API or behavior to document. ### Docs PR URL (required if "docs added" is checked) Paste the PR link from https://github.com/netbirdio/docs here: https://github.com/netbirdio/docs/pull/__  ## Summary by CodeRabbit * **Bug Fixes** * Fixed DNS fallback handling to properly exclude the server's own IP address from the fallback nameserver list, improving DNS resolution reliability in scenarios where fallback servers are needed.  [![Review Change Stack](https://storage.googleapis.com/coderabbit_public_assets/review-stack-in-coderabbit-ui.svg)](https://app.coderabbit.ai/change-stack/netbirdio/netbird/pull/6183?utm_source=github_walkthrough&utm_medium=github&utm_campaign=change_stack)

saavagebueno added the pull-request label 2026-08-05 07:09:07 -04:00

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Reference: DYNR/netbird#27704