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

Summary

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

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.

Environment

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

Steps to Reproduce

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

Expected Behavior

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

Actual Behavior

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

Logs/Evidence

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

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

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.

Proposed Solution

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

Related Issues

ISSUE-2025-001 (MTU reset issue)

Changelog References

CHANGELOG entry: [2025-10-30] - Fixed bridge membership regression after MTU fix deployment. /Users/bogdan/Documents/Workspaces/Xdev/Madagascar/thunderbolts/issues/ISSUE-2025-002.md