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Difficulty: MediumHigh Availability and Redundancy Concepts

During a high-availability failover test on an enterprise subnet, client workstations lose all outbound network connectivity whenever the primary active router is powered off. Network logs confirm that the secondary router successfully assumes the active role within the First Hop Redundancy Protocol (FHRP) group and advertises the virtual MAC address. However, workstations fail to route traffic to external networks until the primary router is brought back online. Which of the following is the primary cause of this connectivity loss?

  1. Workstations were configured with the physical interface IP address of the primary router as their default gateway instead of the FHRP Virtual IP (VIP).Answer
  2. B
    The secondary switch was configured with the highest numerical priority value for the Spanning Tree Protocol (STP) root bridge, placing all uplink ports into a blocking state.
  3. C
    The workstation IP addresses and the default gateway interface were assigned IP addresses on completely different IP subnets.
  4. D
    A native VLAN mismatch across the trunk link between the switches caused all untagged FHRP heartbeat packets to be dropped.

Answer

Workstations were configured with the physical interface IP address of the primary router as their default gateway instead of the FHRP Virtual IP (VIP).
For First Hop Redundancy Protocols (FHRP) like HSRP or VRRP to provide seamless gateway failover, all network endpoints must use the Virtual IP (VIP) as their configured default gateway. If clients are statically or dynamically assigned the physical interface IP of the active router, traffic will continue flowing exclusively to that physical device. When that hardware fails, client traffic drops despite the standby router taking over the FHRP group and virtual MAC address.

Step-by-Step Solution

1
Analyze FHRP operation and failover mechanics
FHRP protocols (such as HSRP or VRRP) group multiple physical routers into a single logical gateway sharing a Virtual IP (VIP) and Virtual MAC address.
For high availability to function seamlessly, end host devices must send default gateway traffic to the VIP rather than individual physical interface IPs.
2
Evaluate the observed failure symptom against host configurations
The secondary router successfully transitioned to active status and answered for the virtual MAC, but workstations remained unable to reach external networks.
This behavior indicates that workstation traffic was targeted directly to the primary router's physical IP address, bypassing the virtual gateway entirely.
3
Identify the misconfiguration cause
The static or DHCP-assigned default gateway setting on workstations was pointing to the primary physical IP (e.g., 10.0.1.2) instead of the virtual IP (e.g., 10.0.1.1).
When the primary router went down, the workstations had no mechanism to dynamically route traffic to the standby router's physical IP.

Key Concept

First Hop Redundancy Protocol Virtual IP Configuration
Estimated Time:1m 30s
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Topics

High Availability and Redundancy Concepts

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