Which of the following statements accurately describes a key difference between HSRP (Hot Standby Router Protocol) and VRRP (Virtual Router Redundancy Protocol)?
Correct Answer: B
Detailed Explanation: HSRP (Hot Standby Router Protocol) and VRRP (Virtual Router Redundancy Protocol) Comparison: Both HSRP and VRRP are designed to provide gateway redundancy, ensuring network connectivity for hosts even if the primary default gateway router fails. They achieve this by creating a virtual router consisting of a group of physical routers. Let's compare them focusing on the aspects relevant to the question and beyond: Active-Standby Operation vs. Active-Active Load Balancing: HSRP (Active-Standby): HSRP primarily operates in an active-standby mode. In an HSRP group, one router is elected as the active router, and it forwards traffic for the virtual router IP address. One or more other routers act as standby routers. Standby routers monitor the active router and are ready to take over if the active router fails. However, in standard HSRP, standby routers do not actively forward traffic for the virtual IP address in normal operation. They are in a passive state, waiting for a failover event. Therefore, standard HSRP does not provide active-active load balancing. It is primarily a failover mechanism. VRRP (Active-Standby Primarily, but can be Active-Active-like with extensions/configurations): VRRP also primarily operates in an active-standby mode by default, similar to HSRP. In a VRRP group, one router becomes the master router (equivalent to HSRP's active router), and others are backup routers (standby). The master router forwards traffic for the virtual router IP, and backups are in standby. However, VRRP has some features or extensions (and vendor-specific implementations) that can be used to achieve a form of active-active-like behavior or load distribution in certain scenarios, even though the base VRRP protocol itself is fundamentally active-standby. These techniques often involve using multiple VRRP groups, with different master routers for different VLANs or groups of hosts. While not inherently active-active within a single VRRP group, VRRP offers more flexibility for distributed configurations that can simulate load sharing across multiple routers by using multiple virtual routers. GLBP (Gateway Load Balancing Protocol - Cisco Proprietary): GLBP (another FHRP from Cisco) is specifically designed to provide active-active load balancing in addition to redundancy. In GLBP, all routers in a GLBP group can actively forward traffic simultaneously for the same virtual IP address. GLBP uses a virtual MAC address and ARP replies to distribute traffic across multiple routers. GLBP is more complex than HSRP or VRRP but offers true active-active load sharing. Protocol Standard vs. Proprietary: HSRP (Cisco Proprietary): HSRP is a Cisco proprietary protocol. While it is widely implemented on Cisco devices and is well-understood, it is not an open standard and is primarily used in Cisco environments. VRRP (Open Standard): VRRP is an open standard protocol (RFC 5798). This means it is defined in an open RFC and can be implemented by multiple vendors (Cisco, Juniper, Huawei, etc.). VRRP's open standard nature makes it more interoperable in multi-vendor environments. IPv6 Support: HSRP and VRRP Both Support IPv6: Both HSRP and VRRP have versions that support IPv6. HSRPv2 and VRRPv3 are the versions that support IPv6, in addition to IPv4. Option A is incorrect because both protocols support IPv6. Advertisement Messages (Hello Messages): HSRP and VRRP Both Use Multicast: Both HSRP and VRRP primarily use multicast for advertisement (hello) messages to communicate between routers in a group. This allows for efficient communication within the group without requiring each router to send individual unicast messages to every other group member. Option D is incorrect as it mischaracterizes the advertisement method. Why Option B is Correct: Accurately Highlights Load Balancing Difference: Option B correctly points out the key difference in load balancing: VRRP, with certain configurations and extensions, can achieve a form of active-active load distribution (though base VRRP is active-standby), while standard HSRP is primarily active-standby and does not provide active-active load balancing within a single group. GLBP is the Cisco FHRP designed specifically for active-active load balancing. Why Other Options are Incorrect: A. HSRP supports IPv6, while VRRP only supports IPv4. Both HSRP and VRRP have IPv6-capable versions. C. HSRP is an open standard protocol, while VRRP is Cisco proprietary. This is the opposite of the truth. HSRP is Cisco proprietary, and VRRP is an open standard. D. VRRP uses multicast for advertisement messages, while HSRP uses unicast. Both HSRP and VRRP primarily use multicast for advertisement messages. In Conclusion: While both HSRP and VRRP provide gateway redundancy through active-standby operation, a key distinction lies in their load balancing capabilities. Standard HSRP is strictly active-standby. VRRP, while also primarily active-standby in its base form, offers more flexibility to achieve active-active-like configurations by using multiple VRRP groups for different traffic sets. GLBP is the Cisco FHRP specifically designed for true active-active load balancing. Understanding these nuances of FHRP protocols is essential for designing highly available networks, and this question tests your knowledge of these functional differences.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.