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Difficulty: HardFirst Hop Redundancy Protocols (HSRP and VRRP)

A network administrator has configured HSRPv2 between two routers, R1 (Active, priority 110, interface tracking decrements priority by 30) and R2 (Standby, priority 100, preemption enabled). Arrange the operational steps in the correct chronological sequence from the moment R1's tracked interface fails until R2 successfully handles traffic as the new Active router.

  1. 1R1 detects the failure of its tracked upstream interface and immediately decrements its configured HSRP priority from 110 to 80.
  2. 2R1 sends an HSRP Hello multicast packet reflecting its newly reduced priority value of 80 to the HSRP group.
  3. 3R2 receives R1's Hello packet, compares its priority (100) to R1's priority (80), and initiates preemption by transmitting an HSRP Coup message.
  4. 4R1 receives the Coup message from R2, relinquishes its Active role, responds with an HSRP Resign message, and transitions to the Standby state.
  5. 5R2 transitions to the Active state and broadcasts a Gratuitous ARP (GARP) frame using the virtual MAC address to update Layer 2 switch forwarding tables.

Answer

The correct chronological order is: 1) R1 detects tracked interface failure and reduces priority to 80; 2) R1 advertises the degraded priority via HSRP Hello; 3) R2 identifies its higher priority and sends an HSRP Coup message; 4) R1 relinquishes active status and broadcasts an HSRP Resign message; 5) R2 assumes the Active state and broadcasts a Gratuitous ARP to update switch CAM tables.
The failover process begins locally on R1 when the tracked link drops, causing priority degradation. Next, R1 informs the segment via Hello packets containing the updated priority. R2 evaluates this priority against its own higher priority and uses its preemption configuration to send a Coup message. R1 acknowledges this by relinquishing control and issuing a Resign message while moving to Standby state. Finally, R2 assumes the Active state and broadcasts a Gratuitous ARP to rewrite switch port bindings for the shared virtual MAC address.

Step-by-Step Solution

1
Identify the initial triggering event
R1's tracked interface drops, reducing R1's priority from 110 to 80.
HSRP interface tracking dynamically recalculates priority immediately upon physical link or line protocol failure.
2
Determine how priority changes are communicated
R1 transmits Hello packets advertising priority 80.
HSRP routers exchange control messages periodically to communicate current group state and priority values.
3
Analyze preemption logic on the standby device
R2 observes R1's priority (80) is lower than R2's (100) and sends a Coup packet.
Preemption allows a router with higher priority than the current Active router to claim the Active role.
4
Trace active router role surrender
R1 transitions to Standby after issuing a Resign packet.
Receiving a valid Coup from a higher-priority router forces the current Active router to yield leadership.
5
Verify Layer 2 forwarding convergence
R2 moves to Active state and emits a Gratuitous ARP.
GARP ensures attached Layer 2 switches immediately rewrite their MAC tables so traffic sent to the virtual IP/MAC reaches R2.

Key Concept

HSRP Preemption and Interface Tracking Convergence Sequence
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Topics

First Hop Redundancy Protocols (HSRP and VRRP)

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