Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureHard
A network engineer is configuring a new Catalyst 9300 switch. The requirement is to ensure that when a critical server's network adapter fails, its backup adapter on a different switch port automatically takes over with minimal disruption, without relying on Spanning Tree Protocol convergence time. Which Layer 2 feature is designed for this fast failover scenario?
- AEtherChannel
- BUDLD
- CFlexLink
- DPVST+
Show answer & explanationAnswer & explanation
Correct answer: C. FlexLink
FlexLink is a Cisco proprietary feature that provides fast failover between a pair of Layer 2 interfaces (a primary and a backup) without relying on STP convergence, making it ideal for critical server connections where sub-second failover is required.
Why the other options are wrong
- A. EtherChannel (or LACP/PAgP) bundles multiple links into one logical link for bandwidth and redundancy, but a single link failure within the bundle is handled differently than a complete adapter/port failure with a hot-standby backup.
- B. UDLD (UniDirectional Link Detection) detects unidirectional links. While important for STP stability, it does not provide the fast failover mechanism for a primary/backup port pair itself.
- D. PVST+ (Per-VLAN Spanning Tree Plus) prevents Layer 2 loops and provides redundancy, but it relies on STP convergence which can take several seconds, failing to meet the 'minimal disruption' and 'without relying on STP convergence' requirements.
FlexLink
FlexLink is a Cisco proprietary Layer 2 feature that allows configuration of a primary and a backup interface pair, enabling rapid failover (sub-second) when the primary link goes down, bypassing Spanning Tree Protocol convergence.
- Cisco proprietary.
- Primary/backup interface pair.
- Sub-second failover.
- Bypasses STP convergence time.
- Used for critical server connections or uplinks.
Memory trick: Flex your links for a fast switch, no STP delay, no hitch.