N10-009 Question 148
Single answerFirst Hop Redundancy Protocol (FHRP) / Virtual IP (VIP)A network administrator is configuring gateway redundancy for a user VLAN with two Layer 3 switches. Hosts on VLAN 20 must keep the same default gateway address even if the active gateway fails. During testing, users report that they should not need any changes to their IP configuration when a failover occurs. Which solution best meets this requirement?
- A
Configure an FHRP so both switches share a virtual IP address that clients use as their default gateway
- B
Assign each switch a different default gateway address and manually change client settings during an outage
- C
Use link aggregation between the two switches so hosts can use either physical gateway IP address interchangeably
- D
Deploy a DHCP reservation for each client so the gateway can be rewritten automatically after a switch failure
Show answer and explanation
Correct answer: A
Explanation
The best answer is to use an FHRP with a virtual IP address that end devices use as their default gateway. This is the standard best practice for default gateway high availability on a subnet. In real deployments, protocols such as HSRP, VRRP, and GLBP allow multiple routers or Layer 3 switches to present a single logical gateway to hosts. When the active gateway fails, another member takes over the VIP and continues forwarding traffic, minimizing user impact. This design aligns with common enterprise networking guidance and vendor documentation for gateway redundancy: hosts should use the VIP, not the physical IP of an individual router or switch, when transparent failover is required.
- A. Correct.
Correct. First Hop Redundancy Protocols such as HSRP, VRRP, and GLBP provide a virtual IP (VIP) and virtual gateway function for end hosts. Clients point to the shared VIP as their default gateway, and if the active device fails, another device in the redundancy group takes over forwarding duties without requiring hosts to change their configuration.
- B. Incorrect.
Incorrect. Using different default gateway addresses on each switch does not provide seamless failover. Clients would need reconfiguration or some other mechanism to move to the surviving gateway, which violates the requirement that users should not need any IP configuration changes during failover.
- C. Incorrect.
Incorrect. Link aggregation increases bandwidth and redundancy for links, but it does not make two different routed gateway IP addresses appear as one default gateway to hosts. FHRP addresses gateway redundancy at Layer 3, whereas link aggregation addresses link redundancy and load sharing at Layer 2/Layer 3 depending on implementation.
- D. Incorrect.
Incorrect. DHCP can provide default gateway information when a lease is issued or renewed, but it is not a fast or reliable failover mechanism for gateway redundancy during an outage. Existing clients would continue using their current gateway until renewal or manual intervention, so this does not meet the requirement for transparent failover.