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Zorluk: OrtaFirst Hop Redundancy Protocols (HSRP and VRRP)

An enterprise LAN uses HSRP for gateway redundancy with interface tracking configured on Router R1 (currently Active). Router R2 is in the Standby state with preemption enabled. When R1's tracked WAN uplink interface fails, a sequence of failover actions takes place. Place the operational steps in the correct chronological order from first to last.

  1. 1Router R1 detects the failure of its tracked WAN uplink interface and decrements its internal HSRP priority value.
  2. 2Router R1 transmits an HSRP Hello packet advertising its newly reduced priority level to the multicast group.
  3. 3Router R2 evaluates the lower priority in R1's Hello packet and sends an HSRP Coup message to claim the Active role.
  4. 4Router R2 transitions to the Active state and broadcasts a Gratuitous ARP (GARP) to update Layer 2 switch forwarding tables.

Cevap

The correct sequence begins with Router R1 detecting the tracked interface failure and decrementing its priority. Next, Router R1 advertises the reduced priority in an HSRP Hello message. Router R2 detects that its priority is now higher and transmits an HSRP Coup message to preempt the Active role. Finally, Router R2 assumes the Active state and broadcasts a Gratuitous ARP to update Layer 2 switch MAC tables.
The chronological order follows the exact functional steps of HSRP failover: local event detection and priority decrement happens first, advertising the lower priority via Hello messages occurs second, preemptive takeover via Coup message happens third, and Layer 2 switch table updates via Gratuitous ARP happen last.

Adım Adım Çözüm

1
Identify the initial trigger event caused by interface tracking.
Router R1 detects the link failure on its monitored interface and immediately subtracts the configured track decrement value from its HSRP priority.
Interface tracking must first process the line protocol state change before modifying the protocol metric.
2
Communicate the updated priority to neighboring HSRP routers.
Router R1 encapsulates its updated (lower) priority into its standard HSRP Hello packet and multicasts it to 224.0.0.2 (or 224.0.0.102 for HSRPv2).
HSRP routers rely on periodic Hello packets to discover neighbor priorities and state changes.
3
Execute preemption election on the standby router.
Router R2 compares its priority against the received Hello priority. Finding its own priority higher, it transmits an HSRP Coup (or Speak/Active assertion) message.
The preemption feature allows a higher-priority router to claim the Active role from a lower-priority Active router.
4
Refresh the Layer 2 network path for client traffic.
Router R2 transitions to the Active state and broadcasts a Gratuitous ARP containing the virtual IP and virtual MAC address mapping.
Layer 2 switches along the LAN segment must update their CAM tables to forward frames destined for the gateway virtual MAC out the port connected to R2.

Anahtar Kavram

HSRP Interface Tracking and Preemption Failover Sequence
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Konular

First Hop Redundancy Protocols (HSRP and VRRP)

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