Below are my notes for the CCNP Routing & Switching SWITCH 300-115 certification exam. I used two Cisco 3560 switches and GNS3 to perform my labs. For theory, I used Cisco Configuration Guides and the Cisco Press Official Certification Guide.
Hot Standby Router Protocol, HSRP, is a Cisco proprietary protocol to make multiple routers or switches appear as one gateway. The gateway is where the redundancy is provided. For each redundant gateway, there is a common HSRP group. One router/switch becomes the primary HSRP router and another is selected as the standby HSRP router. Any other devices part of the group are in the listen HSRP state.
At a 3 second interval, routers send HSRP hello messages to become aware if the other is up or down (between Active and Standby). The hold time value is 10 seconds or three times the hello timer. These hello messages are sent to the multicast address 18.104.22.168 using UDP port 1985.
There can be up to 255 HSRP groups and they are only locally significant.
Election of an active and standby HSRP router is based on a priority value of 0 through 255. By default, the priority is 100 but the highest priority value becomes the active router for the HSRP group. If there is a tie, the router with the highest IP address becomes the active router.
When HSRP is enabled, an interface goes through the following states:
I will use R1 and R2 as the two routers to provide a redundant gateway for 192.168.1.1. [Read more…] about How To Configure HSRP