Verify and repair a potentially corrupted bridge (vmbr0) on a single node.

[dsintayehu]

Environment:

• Proxmox VE 8.4.14
• 3-node cluster: dev-proxhost1, dev-proxhost2, dev-proxhost3
• All nodes use identical bridge and VLAN configurations (main bridge: vmbr0)

Issue Summary:
When a VM is migrated from dev-proxhost1 or dev-proxhost3 to dev-proxhost2, the VM immediately loses network connectivity.

• From within the migrated VM, even the default gateway becomes unreachable.
• The same VMs work perfectly on the other two nodes.
• The issue persists regardless of the VM’s operating system or VLAN tag.

Troubleshooting Performed:

• Verified /etc/network/interfaces — configuration for vmbr0 matches the other nodes.
• Restarted networking service and confirmed no syntax errors.
• Checked for link state and physical NIC status — all appear normal.
• No firewall or VLAN misconfiguration detected.

Observation:
We suspect that vmbr0 on dev-proxhost2 may have become corrupted or misconfigured at a lower level, as even freshly created test VMs on that node exhibit the same behavior.


Question:

• What would be the best approach to verify and repair a potentially corrupted bridge (vmbr0) on a single node?
• Are there known cases in which a bridge appears fine in configuration but fails to pass traffic at the kernel or switching layer?

Thank you in advance for your time and support.

 

[bbgeek17]

Hi @dsintayehu ,

The first step would be to accompany your report with actual saved and running configuration output from "good" and "bad" notes.
I.e. output of:
- cat /etc/network/interfaces
- ip a
- ip route
- brctl show
- ping x.x.xx

Add to it similar output from the VM.
Do any VMs work on host2? I.e. freshly created ones directly on that host? Does the host have normal communication itself? How did you test it? Is MTU consistent? Are switch ports assign to this host configured properly? Did you double/triple check it? Have you checked firewall configuration?

Linux bridge configuration is pretty straightforward and standard. There is nothing proprietary in how PVE does it.

PS make sure to use CODE tags available from the edit menu of the post box.

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