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Difficulty: Very hardFirst Hop Redundancy Protocols (HSRP and VRRP)

A network engineer is configuring first-hop redundancy on router R1's GigabitEthernet0/1 interface, which has been assigned the physical IPv4 address 192.168.20.1/24192.168.20.1/24. The engineer initially attempts to configure HSRP Group 20 using the command `standby 20 ip 192.168.20.1`, but then evaluates migrating the design to VRRPv2 using the command `vrrp 20 ip 192.168.20.1`. Assuming default protocol parameters are used, which operational distinction correctly describes how HSRP and VRRP handle this configuration attempt and default preemption behavior?

  1. HSRP rejects configuring the virtual IP address to match a physical interface IP address, whereas VRRP permits it, automatically assigning a priority of 255 to the IP address owner with mandatory preemption enabled.Answer
  2. B
    HSRP accepts assigning the physical interface IP address as the virtual IP address but disables preemption by default, whereas VRRP rejects any virtual IP configuration that matches an existing physical interface IP.
  3. C
    Both protocols permit assigning the physical interface IP address as the virtual IP address, but HSRP enables preemption by default while VRRP disables preemption by default.
  4. D
    VRRP rejects using the physical interface IP address because VRRP master election requires an unassigned host address, whereas HSRP requires the virtual IP to match the active router's physical interface IP address.

Answer

HSRP rejects configuring the virtual IP address to match a physical interface IP address, whereas VRRP permits it, automatically assigning a priority of 255 to the IP address owner with mandatory preemption enabled.
The correct answer accurately contrasts the Virtual IP assignment constraints and preemption defaults between Cisco HSRP and standard VRRP. HSRP mandates that the virtual IP address must be an unassigned, unique IP within the local subnet and will throw a configuration error if matched to a physical interface address. Furthermore, HSRP preemption is disabled by default. In contrast, VRRP allows the virtual IP address to be identical to a physical interface IP address on the router (making it the IP address owner with priority 255), and VRRP preemption is enabled by default.

Step-by-Step Solution

1
Evaluate HSRP Virtual IP assignment rules
HSRP requires the Virtual IP address to be a unique IP address within the subnet that is NOT assigned to any physical interface on participating routers.
Cisco IOS HSRP prevents IP address duplication on physical interfaces to prevent ARP and routing loop anomalies.
2
Evaluate VRRP Virtual IP assignment rules (IP Address Owner)
VRRP permits the virtual IP address to match the primary physical IPv4 address of an interface.
When a router's interface physical IP matches the VRRP virtual IP, that router acts as the VRRP IP Address Owner and is automatically assigned the maximum priority of 255.
3
Analyze default preemption behavior in HSRP versus VRRP
HSRP preemption is disabled by default, whereas VRRP preemption is enabled by default.
VRRP RFC standards mandate that preemption is enabled out-of-the-box, ensuring a higher priority router always assumes the Master role, especially when priority is 255.

Key Concept

First Hop Redundancy Protocol (FHRP) Virtual IP Assignment and Preemption Defaults
Estimated Time:2m 0s
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Topics

First Hop Redundancy Protocols (HSRP and VRRP)

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