Cisco Certified Network Associate (CCNA) Practice Exam

What is needed for multiple routers to function as a single virtual router?

1. They must have different IP addresses and unique MAC addresses

2. They must share the same IP address and MAC address

3. They must be configured with different routing protocols

4. They must be in different VLANs

The correct answer is: They must share the same IP address and MAC address

For multiple routers to function as a single virtual router, sharing the same IP address and MAC address is crucial. This configuration allows for seamless failover and load balancing between routers, which enhances redundancy and reliability in network communications. When routers are configured to share a common IP and MAC address, they present themselves to the network as one logical device. In scenarios such as Hot Standby Router Protocol (HSRP), Virtual Router Redundancy Protocol (VRRP), or Gateway Load Balancing Protocol (GLBP), a primary and backup router (or multiple active routers) use the same virtual IP address. This setup ensures that if the primary router fails, the secondary router can take over without requiring clients to reconfigure their settings. Options that suggest the need for different IP addresses or MAC addresses would hinder the functionality of virtualization since the routers would be unable to present a unified interface to the network. Using different routing protocols would complicate the routing process instead of consolidating it under a single virtual router, and being in different VLANs would also prevent them from operating as a cohesive entity. Thus, the requirement to share the same IP and MAC addresses facilitates a coherent and resilient network architecture.