In Hot Standby Router Protocol (HSRP), which state indicates that a router is actively forwarding traffic for the virtual IP address?
Correct Answer: D
Detailed Explanation: Hot Standby Router Protocol (HSRP) is a Cisco proprietary redundancy protocol designed to provide high availability for IP networks by ensuring that user traffic immediately and transparently recovers from first hop failures. In an HSRP group, multiple routers work together to present a single virtual router (with its own virtual IP address) to the hosts on a LAN. Only one router in the group is selected to actively forward traffic—the one in the Active state. The Active state in HSRP means that the router is currently handling all traffic destined for the virtual IP address. It is the primary router for the HSRP group. In contrast, the Standby state is held by the router that is next in line; it monitors the active router and will take over if the active router fails. The Listen and Speak states occur during the process of establishing and maintaining HSRP relationships, with routers exchanging hello messages to determine roles and priorities. How HSRP Works: Active Router: The router in the Active state is responsible for forwarding packets that are sent to the virtual IP address. This router is selected based on HSRP priority (a configurable value) and, if there is a tie, the highest IP address. Standby Router: The router in the Standby state monitors the active router’s hello messages. If these messages are missed for a specific period (the hold time), the standby router transitions into the Active state. Hello Packets: Routers in an HSRP group exchange hello packets at regular intervals. These packets help each router keep track of the state of other routers in the group. State Transitions: Upon startup, routers initially enter the HSRP state machine (which includes states like Init, Learn, Listen, Speak, Standby, and Active). The final state for the router that is forwarding traffic is Active. Why the Active State is Critical: The Active state is vital for maintaining continuous network availability. Because the Active router handles the forwarding of traffic, any failure in this router is immediately mitigated by a transition of the Standby router into the Active state. This seamless switchover minimizes downtime and maintains uninterrupted connectivity for hosts using the virtual IP address. Troubleshooting Considerations: When troubleshooting HSRP issues, network administrators often check the HSRP status using commands such as: show standby This command shows the state of each router in the HSRP group, including which router is Active and which is Standby. Misconfigurations, such as incorrect priority settings, can lead to unexpected Active/Standby assignments, so verifying the state is an important step. Conclusion: In HSRP, the router that is currently forwarding traffic for the virtual IP address is in the Active state, making Option D the correct answer. Understanding HSRP state definitions is key to managing network redundancy and ensuring high availability.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.