[PR #4735] [client] Clamp MSS on outbound traffic #4380

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saavagebueno · 2025-11-20T08:08:16-05:00

saavagebueno commented

2025-11-20 08:08:16 -05:00

Original Pull Request: https://github.com/netbirdio/netbird/pull/4735

State: closed
Merged: Yes

Describe your changes

Clamp all outbound TCP SYNs to avoid MTU issues for routed traffic, including container traffic.

Userspace fw clamping can be disabled with the env var NB_DISABLE_MSS_CLAMPING=true

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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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**Original Pull Request:** https://github.com/netbirdio/netbird/pull/4735 **State:** closed **Merged:** Yes --- ## Describe your changes Clamp all outbound TCP SYNs to avoid MTU issues for routed traffic, including container traffic. Userspace fw clamping can be disabled with the env var `NB_DISABLE_MSS_CLAMPING=true` ## Issue ticket number and link ## Stack  ### Checklist - [x] Is it a bug fix - [ ] Is a typo/documentation fix - [x] 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) ### 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/__

saavagebueno added the pull-request label 2025-11-20 08:08:16 -05:00

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Reference: SVI/netbird#4380