Diagnosing a flapping link
A link that dies cleanly is easy. A link that goes up and down every few minutes is maddening — and the cause is almost always physical.
Start at the physical layer
Most flaps are a cable, a connector or an optic: a marginal fibre, a dusty connector, an optic or DAC that is failing or mismatched. Error counters on the port — CRC errors, input errors climbing — point straight at it. A clean swap of the cable or optic resolves a large share of flaps.
Then negotiation
A speed or duplex mismatch, or autonegotiation disagreeing between the two ends, produces exactly this intermittent misery. Link negotiation covers getting both sides to agree. Forcing one end and auto-ing the other is a classic way to create a flap.
What it takes down with it
A flapping link under a bond keeps dropping and re-adding a member; under BGP it churns routes (session health). Fixing the link fixes the symptoms above it. Tell us the port and timestamps and we will read our side's counters and arrange remote hands for a cable or optic swap.
Still stuck? Mail support@novogara.com — an engineer answers, at any hour. Back to the knowledge base