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Network L6 NETWORK-1387 · 15 min

An MLAG pair looks stable and one VLAN blackholes east-west traffic

Most traffic is fine, yet a subtle untagged recovery flow dies because the peer-link native VLAN is no longer aligned between peers.

NetworkFoundation OpsLevel 6Free15 min
Scenario

A template standardization lands and later orphan or recovery traffic fails only under MLAG peer-link fallback conditions.

What to check first
  • Identify the primary failure signal in the The Fabric Was Tagged Correctly Except for the One Untagged Path Nobody Expected to Matter scenario.
  • Separate visible symptoms from the underlying technical dependency.
  • Describe the safest recovery path and the follow-up prevention work.
Checking checklist
  1. Summarize the current impact and the last known change.
  2. Collect direct evidence from logs, runtime state, and configuration before changing anything.
  3. Separate immediate recovery from permanent prevention work.
Recovery and prevention

Validate peer-link native VLAN behavior before tuning spanning-tree or rehoming workloads.

Questions worth viewing together
What should you verify first when An MLAG pair looks stable and one VLAN blackholes east-west traffic appears?

Community-field network problem inspired by MLAG community cases where peer-link native VLAN drift broke an orphan recovery path. Native VLAN drift hides until an untagged recovery path is the only path left.

What usually causes An MLAG pair looks stable and one VLAN blackholes east-west traffic in production?

Teams often blame host NIC bonding when the peer-link native VLAN mismatch is what broke the failover path.

What should you document after resolving An MLAG pair looks stable and one VLAN blackholes east-west traffic?

MLAG peer-link templates should treat native VLAN values as critical recovery-path settings, not cosmetic defaults.