[PR #5805] [client] Fix ICE reconnection loop and buffer candidates before agent initialization #26813

New Issue

saavagebueno · 2026-08-05T07:07:50-04:00

saavagebueno commented

2026-08-05 07:07:50 -04:00

Original Pull Request: https://github.com/netbirdio/netbird/pull/5805

State: closed
Merged: No

Summary

Guard Loop Fix: When both peers are behind the same NAT (same public IP), their connectivity guards fire simultaneously every ~12s, each sending a new offer with a new session ID. This cancels the other side's ICE agent before it can finish negotiating, creating an infinite reconnection loop. Fix: skip new offers while agentConnecting == true to let the current ICE attempt complete.
Candidate Buffering: Remote ICE candidates that arrive before the local ICE agent is created were silently dropped. Add a pendingCandidates buffer that collects early candidates and flushes them once the agent is ready.

Both fixes are tightly coupled — without the buffer, the guard loop fix alone would still miss early candidates.

Checklist

Bug fix
Create tests that fail without the change: ICE connections between peers behind the same NAT consistently failed before this fix
Documentation not needed — internal ICE behavior change, no user-facing API change

By submitting this pull request, I confirm that I have read and agree to the terms of the Contributor License Agreement.

Fixes #3669 — Unable to connect to netbird peer on different LAN with the same public IP
Fixes #5672 — ICE Agent is not initialized yet on android app
Related #2703 — Multiple peers behind NAT getting relayed
Related #3339 — Same LAN cannot successfully P2P
Related #4031 — No P2P/direct connection, only relayed
Related #4225 — Netbird Self-Hosted P2P not working
Related #5670 — macOS ICE agent never initializes (arm64)

Summary by CodeRabbit

Bug Fixes
- Buffer early remote connection candidates with a bounded cap to avoid lost candidates and limit memory use.
- Expand and queue applicable server-reflexive candidates for later delivery instead of dropping them.
- Prevent rapid reconnection churn by skipping replacement of a recently-started agent while it’s still connecting (adds a short protection window).
- Flush buffered candidates into a newly created connection and clear the buffer on close to prevent stale data.

**Original Pull Request:** https://github.com/netbirdio/netbird/pull/5805 **State:** closed **Merged:** No --- ## Summary - **Guard Loop Fix**: When both peers are behind the same NAT (same public IP), their connectivity guards fire simultaneously every ~12s, each sending a new offer with a new session ID. This cancels the other side's ICE agent before it can finish negotiating, creating an infinite reconnection loop. Fix: skip new offers while `agentConnecting == true` to let the current ICE attempt complete. - **Candidate Buffering**: Remote ICE candidates that arrive before the local ICE agent is created were silently dropped. Add a `pendingCandidates` buffer that collects early candidates and flushes them once the agent is ready. Both fixes are tightly coupled — without the buffer, the guard loop fix alone would still miss early candidates. ## Checklist - [x] Bug fix - [x] Create tests that fail without the change: ICE connections between peers behind the same NAT consistently failed before this fix - [x] Documentation not needed — internal ICE behavior change, no user-facing API change By submitting this pull request, I confirm that I have read and agree to the terms of the [Contributor License Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md). ## Related Issues Fixes #3669 — Unable to connect to netbird peer on different LAN with the same public IP Fixes #5672 — ICE Agent is not initialized yet on android app Related #2703 — Multiple peers behind NAT getting relayed Related #3339 — Same LAN cannot successfully P2P Related #4031 — No P2P/direct connection, only relayed Related #4225 — Netbird Self-Hosted P2P not working Related #5670 — macOS ICE agent never initializes (arm64)  ## Summary by CodeRabbit * **Bug Fixes** * Buffer early remote connection candidates with a bounded cap to avoid lost candidates and limit memory use. * Expand and queue applicable server-reflexive candidates for later delivery instead of dropping them. * Prevent rapid reconnection churn by skipping replacement of a recently-started agent while it’s still connecting (adds a short protection window). * Flush buffered candidates into a newly created connection and clear the buffer on close to prevent stale data.

saavagebueno added the pull-request label 2026-08-05 07:07:50 -04:00

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Reference: DYNR/netbird#26813