Question

Difficulty: MediumFirst Hop Redundancy Protocols (HSRP and VRRP)

A network administrator is designing a First Hop Redundancy Protocol (FHRP) deployment for a LAN segment. The design requirement dictates that the virtual default gateway IP address configured for host devices must be identical to the physical IP address assigned to the primary router's GigabitEthernet0/0 interface. Which protocol selection and operational characteristic accurately satisfies this design requirement?

  1. VRRP, because it permits the virtual IP address to match a physical interface IP address, making that router the IP address owner with a default priority of 255.Answer
  2. B
    HSRP version 1, because configuring an interface physical IP address as the standby IP address automatically elevates the router priority to 255.
  3. C
    HSRP version 2, because HSRPv2 updated its virtual MAC format to allow physical IP address mapping for backward compatibility.
  4. D
    Both HSRP and VRRP, because both protocols natively allow assigning an active router's physical IP address as the virtual gateway address.

Answer

VRRP allows the virtual IP address to match a router's physical interface IP address, designating that router as the IP address owner with an effective priority of 255.
In VRRP, a router can be configured to use its own physical interface IP address as the virtual IP address for the redundancy group. When this occurs, the router becomes the IP address owner and its priority is fixed at 255, ensuring it acts as the Master router whenever its interface is active.

Step-by-Step Solution

1
Analyze the FHRP requirement for IP address ownership.
The scenario requires the virtual default gateway IP address to be identical to the primary router's physical interface IP address.
Different FHRP protocols have distinct rules regarding whether the virtual IP address can overlap with an interface's assigned physical IP.
2
Evaluate HSRP (v1 and v2) behavior regarding physical IP address assignment.
HSRP requires the virtual IP address to be a unique IP address on the subnet that is not assigned to any physical interface of the participating routers.
Attempting to assign a physical IP address as the HSRP virtual IP results in a CLI configuration error in Cisco IOS.
3
Evaluate VRRP (v2 and v3) behavior regarding physical IP address assignment.
VRRP explicitly supports assigning the physical interface IP address of a router as the VRRP virtual IP address.
When a router's physical IP matches the VRRP virtual IP, that router assumes the role of IP Address Owner and its operational priority is automatically set to 255 (the maximum possible priority).

Key Concept

VRRP IP Address Ownership vs HSRP Virtual IP Restrictions
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