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Difficulty: MediumHigh Availability and Redundancy Concepts

A network administrator configures a pair of routers using a First Hop Redundancy Protocol (FHRP) to ensure high availability for a subnet. During scheduled maintenance on the primary router, the secondary router successfully assumes the active role according to the system logs. However, workstations on the subnet immediately lose access to external networks. Which of the following is the most likely cause of this connectivity failure?

  1. Workstations were configured with the physical IP address of the primary router as their default gateway instead of the shared virtual IP address.Answer
  2. B
    The secondary router was configured with a higher Spanning Tree Protocol (STP) priority value, causing the switch port to block traffic.
  3. C
    The hosts were assigned APIPA addresses because the secondary router failed to forward DHCP relay requests during failover.
  4. D
    The primary router was configured with an implicit deny rule in its ACL that blocked preemptive virtual MAC address generation.

Answer

Workstations were configured with the physical IP address of the primary router as their default gateway instead of the shared virtual IP address.
First Hop Redundancy Protocols rely on clients directing default gateway traffic to a designated Virtual IP (VIP). If workstations are manually or dynamically configured with the physical IP address of one router, failover mechanisms will not redirect host traffic when that specific physical router goes offline.

Step-by-Step Solution

1
Analyze the FHRP deployment model and host default gateway assignments.
FHRP protocols (such as HSRP or VRRP) create a single shared Virtual IP (VIP) and Virtual MAC address for host redundant default gateway operations.
For high availability to function seamlessly, end devices must point to the Virtual IP rather than any single physical router interface IP address.
2
Evaluate the reported symptom against host network settings.
Although the secondary router transitioned to active state correctly, host traffic reached a dead physical IP address because clients targeted the physical interface IP of the primary router.
If hosts use a physical IP, traffic destined for external networks fails as soon as that physical router is taken offline.

Key Concept

FHRP Virtual IP vs Physical IP Gateway Configuration
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Topics

High Availability and Redundancy Concepts

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