Module Practice and Quiz

9.3.1

What did I learn in this module?

First Hop Redundancy Protocols

If a router or router interface that serves as a default gateway fails, the hosts configured with that default gateway are isolated from outside networks. FHRP provides alternate default gateways in switched networks where two or more routers are connected to the same VLANs. One way to prevent a single point of failure at the default gateway, is to implement a virtual router. With a virtual router, multiple routers are configured to work together to present the illusion of a single router to the hosts on the LAN. When the active router fails, the redundancy protocol transitions the standby router to the new active router role. These are the steps that take place when the active router fails:

  1. The standby router stops seeing Hello messages from the forwarding router.
  2. The standby router assumes the role of the forwarding router.
  3. Because the new forwarding router assumes both the IPv4 and MAC addresses of the virtual router, the host devices see no disruption in service.

The FHRP used in a production environment largely depends on the equipment and needs of the network. These are the options available for FHRPs:

  • HSRP and HSRP for IPv6
  • VRRPv2 and VRRPv3
  • GLBP and GLBP for IPv6
  • IRDP

HSRP

HSRP is a Cisco-proprietary FHRP designed to allow for transparent failover of a first-hop IP device. HSRP is used in a group of routers for selecting an active device and a standby device. In a group of device interfaces, the active device is the device that is used for routing packets; the standby device is the device that takes over when the active device fails, or when pre-set conditions are met. The function of the HSRP standby router is to monitor the operational status of the HSRP group and to quickly assume packet-forwarding responsibility if the active router fails. The router with the highest HSRP priority will become the active router. Preemption is the ability of an HSRP router to trigger the re-election process. With preemption enabled, a router that comes online with a higher HSRP priority will assume the role of the active router. HSRP states include initial, learn, listen, speak, and standby.

9.3.2 Module Quiz – FHRP Concepts