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Zorluk: OrtaFirst Hop Redundancy Protocols (HSRP and VRRP)

A network engineer has configured VRRPv2 between Router A (Master) and Router B (Backup) to provide default gateway redundancy for hosts on VLAN 10. Router A suddenly loses power and stops functioning. What is the correct sequence of operational events from the initial failure of Router A to the complete restoration of host traffic flow through Router B?

  1. 1Router A stops transmitting VRRP Master Advertisement multicast frames onto VLAN 10.
  2. 2The Master_Down_Interval timer on Router B expires after three missed advertisement intervals plus skew time.
  3. 3Router B transitions its internal state from Backup to Master.
  4. 4Router B broadcasts a Gratuitous ARP (GARP) frame mapping the VRRP virtual IP to its virtual MAC address.
  5. 5Layer 2 switches update their MAC address tables to forward host traffic destined for the virtual MAC to Router B.

Cevap

The correct sequence of events is: 1) Router A stops transmitting VRRP Master Advertisement multicast frames. 2) The Master_Down_Interval timer on Router B expires after three missed intervals plus skew time. 3) Router B transitions its internal state from Backup to Master. 4) Router B broadcasts a Gratuitous ARP (GARP) frame mapping the VRRP virtual IP to its virtual MAC address. 5) Layer 2 switches update their MAC address tables to forward host traffic to Router B.
During a VRRP Master router failure, the active Master first stops transmitting VRRP advertisement multicast messages. The Backup router notices the missing messages and waits until its Master_Down_Interval timer (calculated as 3 x Advertisement Interval + Skew Time) expires. When the timer elapses, the Backup router transitions into the Master state. Immediately after becoming Master, it broadcasts a Gratuitous ARP (GARP) packet containing the virtual IP and virtual MAC address. Connected Layer 2 switches receive this GARP and update their MAC address tables so that outbound host traffic destined for the virtual default gateway is properly directed to the new Master router.

Adım Adım Çözüm

1
Identify the initial link/device failure event.
Router A fails and immediately ceases broadcasting VRRP Master Advertisement messages to multicast address 224.0.0.18.
Power loss prevents Router A from generating periodic advertisement packets.
2
Determine the backup router timer monitoring phase.
Router B detects silence on VLAN 10 and waits for the Master_Down_Interval timer (3 * Advertisement_Interval + Skew_Time) to expire.
The timer ensures transient network delays do not trigger unneeded master election failovers.
3
Analyze the state transition on the backup router.
Once the Master_Down_Interval timer expires, Router B moves from Backup state to Master state.
VRRP finite state machine rules require a Backup router to assume Master status if advertisements stop.
4
Identify how the new Master announces its presence to Layer 2 infrastructure.
Router B broadcasts a Gratuitous ARP frame containing the virtual IP and virtual MAC address across the segment.
Notifies connected Layer 2 switches that frames sent to the virtual MAC address should be delivered to Router B's port.
5
Trace the Layer 2 forwarding table update and traffic resumption.
Switches update their MAC address tables and forward subsequent host gateway traffic to Router B.
Hosts continue sending packets to the unchanged virtual MAC, which switches now forward to Router B.

Anahtar Kavram

VRRP Master Failover and Convergence Sequence
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Konular

First Hop Redundancy Protocols (HSRP and VRRP)

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