A network administrator is troubleshooting an intermittent first-hop gateway issue on a du… — Cisco CCNA

A network administrator is troubleshooting an intermittent first-hop gateway issue on a dual-homed router pair ( $R1$ and $R2$ ) providing redundancy for VLAN 50 ( $172.20.50.0/24$ ). $R1$ is intended to be the active HSRP router under normal operational conditions.

The interface configurations are shown below:

text
R1# show running-config interface GigabitEthernet0/1
interface GigabitEthernet0/1
ip address 172.20.50.2 255.255.255.0
standby 50 ip 172.20.50.1
standby 50 priority 115
standby 50 track GigabitEthernet0/0 20

R2# show running-config interface GigabitEthernet0/1
interface GigabitEthernet0/1
ip address 172.20.50.3 255.255.255.0
standby 50 ip 172.20.50.1
standby 50 priority 105
standby 50 preempt

When the uplink interface GigabitEthernet0/0 on $R1$ fails, $R1$ 's priority drops from 115 to 95 ( $115 - 20$ ), allowing $R2$ (priority 105, preemption enabled) to take over as the Active router. However, when GigabitEthernet0/0 on $R1$ recovers and its priority returns to 115, $R2$ remains the Active router and $R1$ stays in Standby state.

Which configuration change on $R1$ will resolve this issue so that $R1$ automatically reclaims the Active HSRP role upon link recovery?

Configure standby 50 preempt under interface GigabitEthernet0/1 on R1.Answer
B
Configure standby 50 ip 172.20.50.2 on R1 so the virtual IP matches its physical interface IP address.
C
Increase the interface tracking decrement value on R1 from 20 to 30 using standby 50 track GigabitEthernet0/0 30.
D
Change the standby group number on R1 to match the priority value using standby 115 ip 172.20.50.1.

Answer

Enabling preemption on R1 using the command 'standby 50 preempt' allows R1 to reclaim the Active gateway role after its tracked interface recovers.

By default, HSRP preemption is disabled. Even if a router has a higher priority than the current Active router, it will not attempt to take over the Active role unless preemption is explicitly configured using the 'standby <group> preempt' command. On R1, once its tracked interface recovered, its priority returned to 115 (higher than R2's 105), but because preemption was missing on R1, it remained in the Standby state. Adding 'standby 50 preempt' to R1 resolves the issue.

Step-by-Step Solution

Analyze initial HSRP priorities and roles

R1 has priority 115 and R2 has priority 105. R1 is Active.

Higher priority determines the Active HSRP router.

Evaluate failover behavior when R1's tracked interface fails

R1 priority drops to 95 (115 - 20). R2 has priority 105 and 'standby 50 preempt' enabled, so R2 takes over as Active.

R2 has preemption enabled and its priority (105) is now higher than R1's reduced priority (95).

Evaluate recovery behavior when R1's tracked interface comes back up

R1 priority returns to 115, but R1 remains Standby because it lacks the 'standby 50 preempt' command.

Without preemption explicitly configured, an HSRP router with a higher priority will not preempt an already operational Active router.

Determine the required configuration fix

Adding 'standby 50 preempt' to R1 allows it to preempt R2 (115 > 105) once priority is restored upon link recovery.

Preemption must be enabled on the router that needs to reclaim the Active state.

Key Concept

HSRP Preemption and Interface Tracking Mechanics

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Step-by-Step Solution

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Common Mistakes

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