An enterprise infrastructure uses two Layer 3 switches, Router-Alpha and Router-Beta, conf… — CompTIA Network+

An enterprise infrastructure uses two Layer 3 switches, Router-Alpha and Router-Beta, configured with Hot Standby Router Protocol (HSRP) to provide default gateway redundancy for hosts on VLAN 50 ( $172.16.50.0/24$ ). Router-Alpha is intended to be the primary gateway and is configured with an HSRP priority of $120$ , preemption enabled, and WAN interface tracking with a priority decrement of $30$ . Router-Beta is configured with an HSRP priority of $100$ . During an unexpected WAN uplink disruption on Router-Alpha, its tracked interface goes down, successfully reducing its advertised priority to $90$ . However, network monitoring reveals that host traffic on VLAN 50 continues routing through Router-Alpha's degraded path instead of transitioning to Router-Beta. Which configuration deficiency on Router-Beta prevents it from assuming the Active gateway role?

Router-Beta does not have preemption enabled in its HSRP configuration, causing it to remain in Standby state as long as Router-Alpha continues transmitting hello packets.Cevap
B
Host computers on VLAN 50 were assigned Router-Alpha's physical interface IP address as their default gateway rather than the shared Virtual IP (VIP) address.
C
The connected access switch port for Router-Beta was placed into a blocking state by Spanning Tree Protocol (STP) due to a Root Bridge priority tiebreaker failure.
D
The HSRP virtual MAC address on Router-Beta was statically locked to Router-Alpha's hardware MAC address during primary initialization.

Cevap

Router-Beta does not have preemption enabled in its HSRP configuration, causing it to remain in Standby state as long as Router-Alpha continues transmitting hello packets.

In First Hop Redundancy Protocols such as HSRP and VRRP, interface tracking decrements a primary router's priority when a monitored uplink fails. If the primary router remains online, it continues broadcasting hello frames with its newly reduced priority. For a backup or standby router to seize the Active role from an operational router with a lower priority, preemption MUST be enabled on the backup/standby router. Without preemption on the standby router, it will only become Active if the primary router completely stops transmitting hello packets.

Adım Adım Çözüm

Analyze initial HSRP priorities and roles.

Router-Alpha has priority

120

(Active) and Router-Beta has priority

100

(Standby).

The router with the higher priority value wins the HSRP Active election.

Evaluate the effect of interface tracking when the WAN uplink fails.

Router-Alpha's priority drops by

30

, resulting in a new priority of

120 - 30 = 90

Interface tracking decrements the active router's priority value upon link failure to trigger failover.

Determine HSRP preemption behavior on the Standby router.

Router-Beta's priority (

100

) is now higher than Router-Alpha's priority (

90

), but Router-Alpha is still sending HSRP hello messages.

Without preemption enabled on Router-Beta, a Standby router will never forcibly take over the Active role from an operational Active router, even if the Active router's priority drops below that of the Standby router.

Anahtar Kavram

First Hop Redundancy Protocol (FHRP) Priority, Preemption, and Interface Tracking

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Adım Adım Çözüm

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