ACSP AOS-CX VSF and VSX 3 — Questions and Answers
Question 1: In AOS-CX VSX, what is the primary purpose of the Inter-Switch Link (ISL)?
- To carry keepalive heartbeat messages only
- To synchronize control-plane state and pass data traffic between VSX peers (Correct answer)
- To provide out-of-band management connectivity
- To carry STP BPDUs between peers
Correct answer: To synchronize control-plane state and pass data traffic between VSX peers
The ISL carries both synchronized control-plane state (MAC tables, ARP, routing) and acts as a data-plane path when traffic must traverse between VSX peers.
Question 2: What happens to VSX operations if the keepalive link fails but the ISL remains up?
- VSX enters split-brain mode immediately
- Operations continue normally because the ISL is the primary health link (Correct answer)
- Both peers reboot to re-elect primary
- MCLAG links on both peers go down
Correct answer: Operations continue normally because the ISL is the primary health link
When only the keepalive fails, VSX continues normally since the ISL remains up and is used for both state sync and peer-alive detection.
Question 3: Which VSX role is elected based on the configured priority value, with a higher number winning?
- Secondary
- Active
- Primary (Correct answer)
- Conductor
Correct answer: Primary
The VSX Primary role is elected based on priority; the switch with the higher configured priority becomes Primary and typically owns the active gateway functions.
Question 4: In VSX, what is the Active Gateway feature used for?
- Providing a shared virtual IP and MAC so both VSX peers can route traffic locally (Correct answer)
- Electing the primary VSX switch
- Synchronizing OSPF adjacencies across the ISL
- Managing keepalive intervals
Correct answer: Providing a shared virtual IP and MAC so both VSX peers can route traffic locally
Active Gateway assigns both VSX peers the same virtual IP and virtual MAC, allowing each peer to locally route traffic without bouncing across the ISL.
Question 5: When configuring a VSX MCLAG (Multi-Chassis LAG), what must be consistent on both VSX peers for the LAG to function correctly?
- Interface speed must be identical on both peers
- The LACP system-ID and port-channel configuration must match (Correct answer)
- STP port cost must be set to 0 on both peers
- Both peers must use the same physical uplink count
Correct answer: The LACP system-ID and port-channel configuration must match
MCLAG requires the same LACP system-ID (configured as VSX system-MAC) and matching port-channel parameters on both peers so the downstream device sees a single logical LAG.
Question 6: In a VSX split-brain scenario where the ISL and keepalive both fail, which peer continues forwarding traffic?
- The Secondary peer shuts down its MCLAG interfaces (Correct answer)
- Both peers continue forwarding identically
- The Primary peer shuts down its MCLAG interfaces
- A third-party arbitrator device decides
Correct answer: The Secondary peer shuts down its MCLAG interfaces
In split-brain, VSX designates the Secondary peer to shut down its MCLAG interfaces, ensuring the Primary peer continues forwarding and avoiding duplicate traffic.
Question 7: Which AOS-CX command verifies that VSX peers are synchronized and shows the synchronization status of routing protocols?
- show vsx status (Correct answer)
- show redundancy peers
- show fabric sync detail
- show lacp peer
Correct answer: show vsx status
The 'show vsx status' command displays the VSX peer state, ISL and keepalive status, and which protocols are currently synchronized between peers.
ACSP AOS-CX VSF and VSX 3
In AOS-CX VSX, what is the primary purpose of the Inter-Switch Link (ISL)?