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Difficulty: MediumHigh Availability and Redundancy Concepts

An enterprise network uses two routers, Router-A and Router-B, to provide default gateway redundancy for the 192.168.50.0/24192.168.50.0/24 subnet using Hot Standby Router Protocol (HSRP). Router-A has a physical interface IP address of 192.168.50.2192.168.50.2, Router-B has a physical interface IP address of 192.168.50.3192.168.50.3, and the configured HSRP virtual IP (VIP) is 192.168.50.1192.168.50.1. During scheduled maintenance, Router-A is rebooted, causing Router-B to successfully transition from Standby to Active status. However, hosts on the 192.168.50.0/24192.168.50.0/24 subnet immediately lose all outbound network access. Which of the following is the most likely cause of this issue?

  1. The host workstations were statically assigned the physical interface IP address 192.168.50.2192.168.50.2 as their default gateway instead of the virtual IP address 192.168.50.1192.168.50.1.Answer
  2. B
    Spanning Tree Protocol designated Router-B as the root bridge because Router-B was configured with a higher numerical priority value than Router-A.
  3. C
    The workstation clients and the virtual gateway address belong to different logical IP subnets due to an incorrect subnet mask assignment.
  4. D
    Router-B rejected host frames because devices on the subnet were not configured with Inter-VLAN routing encapsulation tags for default gateway communication.

Answer

The host workstations were statically assigned the physical interface IP address 192.168.50.2 as their default gateway instead of the virtual IP address 192.168.50.1.
First Hop Redundancy Protocols like HSRP, VRRP, and CARP provide default gateway redundancy by presenting a shared Virtual IP (VIP) address to client hosts. When Router-A reboots, Router-B takes over ownership of the VIP (192.168.50.1192.168.50.1). However, if host workstations were misconfigured to use Router-A's physical interface IP address (192.168.50.2192.168.50.2) as their default gateway, their outbound packets continue targeting 192.168.50.2192.168.50.2, which is currently unreachable, leading to complete outbound access failure.

Step-by-Step Solution

1
Analyze the HSRP topology configuration
Router-A physical IP = 192.168.50.2192.168.50.2, Router-B physical IP = 192.168.50.3192.168.50.3, Virtual IP (VIP) = 192.168.50.1192.168.50.1.
First Hop Redundancy Protocols (FHRP) create a shared Virtual IP (VIP) that acts as the single logical default gateway address for client devices.
2
Evaluate host traffic behavior during failover
Router-B became Active and claimed control of the VIP (192.168.50.1192.168.50.1), but host traffic stopped flowing.
If hosts send packets directly to 192.168.50.2192.168.50.2 (Router-A's physical interface), those packets will be dropped when Router-A reboots, because Router-B only listens for ARP and traffic destined for the VIP (192.168.50.1192.168.50.1) and its own physical IP (192.168.50.3192.168.50.3).
3
Identify the root cause of the misconfiguration
Host default gateway addresses were set to Router-A's physical IP address instead of the HSRP VIP.
To benefit from high availability gateway redundancy, all network clients must point to the Virtual IP address as their default gateway.

Key Concept

First Hop Redundancy Protocol (FHRP) Virtual IP Assignment
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Topics

High Availability and Redundancy Concepts

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