# Thunderbolt Interfaces Not in Bridge After MTU Fix

## Issue ID: ISSUE-2025-002

**Status:** closed  
**Priority:** high  
**Created:** 2025-10-30  
**Updated:** 2025-10-30  
**Assigned to:** unassigned

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## Summary

After applying the MTU fix, thunderbolt interfaces are no longer members of the thunderbridge.

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## Description

Following the deployment of the MTU persistence fix (post-up hooks in interfaces.d), the thunderbolt interfaces failed to join the thunderbridge after `systemctl restart networking`. This regression broke cluster connectivity via thunderbolt.

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## Environment

- **Affected nodes:** baobab, ebony, tapia
- **Component:** network (thunderbolt bridging)
- **Version/software:** Proxmox VE 8.x, ifupdown2, systemd services

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## Steps to Reproduce

1. Deploy MTU fix with post-up hooks in `/etc/network/interfaces.d/10-thunderbolt`.
2. Run `systemctl restart networking`.
3. Check `bridge link show` - thunderbolt interfaces not in thunderbridge.

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## Expected Behavior

Thunderbolt interfaces should remain in thunderbridge with MTU 65520 after networking restart.

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## Actual Behavior

Interfaces have correct MTU but are not added to the bridge, causing loss of cluster connectivity.

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## Logs/Evidence

```
# After restart networking
$ bridge link show
(no thunderbolt interfaces listed)

$ ip link show thunderbolt0
thunderbolt0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65520 ...
```

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## Investigation Notes

- 2025-10-30: Root cause identified - ifupdown2 brings up interfaces but systemd enlist services don't re-trigger on networking restart. Defense-in-depth needed.
- 2025-10-30: Added `post-up ip link set dev $IFACE master thunderbridge || true` to interfaces.d files.

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## Proposed Solution

Add bridge membership to post-up hooks in `/etc/network/interfaces.d/10-thunderbolt` for all nodes.

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## Related Issues

- ISSUE-2025-001 (MTU reset issue)

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## Changelog References

- CHANGELOG entry: [2025-10-30] - Fixed bridge membership regression after MTU fix deployment.</content>
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