Networking FHRP Protocols
FHRP (First Hop Redundancy Protocol) is a set of protocols used to provide high availability and reliability in networks. Here's a comprehensive explanation of the most commonly used FHRP protocols: HSRP, VRRP, and GLBP:
- HSRP, developed by Cisco Systems, is a widely used FHRP protocol for ensuring high availability in IP networks.
- It operates by allowing multiple routers to work together in a group, with one router designated as the active router and others as standby routers.
- The active router forwards packets for the virtual IP address configured on the group, while standby routers monitor the health of the active router.
- HSRP routers communicate using hello packets to detect failures and facilitate failover if needed.
- It provides fast failover times, typically within seconds, minimizing network disruption in the event of a primary router failure.
- HSRP supports multiple versions, including HSRPv1 and HSRPv2, with improvements in authentication and IPv6 support in the latter. 
- VRRP is an open standard protocol defined in RFC 3768, designed to achieve redundancy similar to HSRP but with vendor interoperability.
- Like HSRP, VRRP enables multiple routers to work together to provide redundancy for a virtual IP address.
- VRRP routers elect a master router based on priority, with the highest priority router serving as the master and others as backups.
- It supports IPv4 and IPv6, making it suitable for modern heterogeneous networks.
- VRRP routers exchange advertisement messages to monitor the master router's status and trigger failover if necessary. - VRRP provides load sharing capabilities by allowing routers to be configured with different priorities, influencing the election of the master router. 
- GLBP, also developed by Cisco Systems, combines redundancy with load balancing to optimize network resource utilization.
- Unlike HSRP and VRRP, GLBP distributes traffic across multiple routers, known as active virtual forwarders (AVFs), within a group. - GLBP routers share the virtual IP address, but each AVF has a unique virtual MAC address, allowing for load balancing at the MAC layer.
- It supports different load-balancing algorithms, including round-robin and weighted load balancing, based on configured parameters.
- GLBP routers communicate using hello messages to elect an active virtual gateway (AVG) responsible for forwarding traffic to the virtual IP address.
- In addition to redundancy, GLBP enhances network scalability by efficiently utilizing multiple router resources and optimizing traffic distribution. 
