Cisco Certified Network Associate (CCNA) Practice Exam

In GLBP, which router will respond to client ARP requests?

1. The active virtual gateway will reply with one of four possible virtual MAC addresses.

2. All GLBP member routers will reply in round-robin fashion.

3. The active virtual gateway will reply with its own hardware MAC address.

4. The GLBP member routers will reply with one of four possible burned in hardware addresses.

The correct answer is: The active virtual gateway will reply with one of four possible virtual MAC addresses.

In GLBP (Gateway Load Balancing Protocol), the active virtual gateway plays a crucial role in responding to ARP requests from clients. When a client sends an ARP request to resolve the IP address of the virtual router (the GLBP virtual IP), it is the active virtual gateway that responds. This response includes one of the four possible virtual MAC addresses that are assigned to the GLBP group. These virtual MAC addresses allow for load balancing among the multiple routers in the GLBP group. When clients ARP for the virtual IP, they receive one of these virtual MAC addresses instead of a single router's hardware MAC address, thus enabling the GLBP protocol to distribute traffic effectively across multiple routers and ensure reliability in the event of a failure. This functionality provides both load balancing and redundancy, as the clients recognize the virtual MAC address as valid, regardless of which physical router in the group is currently active. This method prevents any single point of failure and increases the availability of network services.