Last Updated on August 1, 2021 by Admin 2
Which next-hop router redundancy protocol provides backup for an assigned real IP address?
Using VRRP, the shared address of the next-hop router redundancy group can be the real address of a router interface.
Virtual Router Redundancy Protocol (VRRP) is defined in RFC 2338. VRRP enables a group of routers to form a single virtual router, known as a VRRP group. Routers are configured in VRRP groups to provide redundancy for an IP address shared among members of the VRRP group. This address can be the real address of a router interface or a virtual address (or addresses) shared by the group. Each group is comprised of a master and one or more backup routers. If the shared address is the real IP address of a router, that router will always be the master when the address is available. The master router is responsible for forwarding packets sent to the virtual router. The backup routers provide redundancy and stand ready to assume the role of the master router in the event that it is unable to forward packets.
The master virtual router owns the VRRP IP address and is responsible for handling all packets sent to the VRRP IP address. Backup VRRP routers monitor for hello activity from the master virtual router. The master router will advertise using IP 220.127.116.11 and MAC 0000.0c00.01xx (xx is the VRRP Group ID). The advertisements by default will be sent every second, and the master down interval is three seconds.
If the VRRP IP address is NOT the physical address of one of the VRRP routers, then the router with the highest priority will assume the role of the master. The configurable priority range is from 0 to 255, and the default value is 100. The higher the value is, the higher the priority is. If activity stops for the duration of the master router’s down interval, the backup router with the highest priority will become the master router. When the old master router comes back online, it will assume the master role again if it still has the highest priority among all routers.
In the configuration shown below, Router A will be the master router unless it goes down, in which case B will take over. If A comes back up it will assume the master role again.
routerA(config-if)# vrrp 3 priority 130 routerB(config-if)# vrrp 3 priority 110
Hot Standby Router Protocol (HSRP) defines a set of routers that work together to represent one virtual, fault-tolerant router. Thus, redundancy is provided in the event that any one of the routers fails. The shared address of the next-hop router redundancy group is not the real address of a router interface.
Gateway Load Balancing Protocol GLBP) is a Cisco-designed protocol that provides for the dynamic utilization of redundant routers in a broadcast network. The shared address of the next-hop router redundancy group is not the real address of a router interface. A virtual group address is used.
Configure and verify first-hop redundancy protocols