| To pass the BSCI exam, you need to know the | | | | one doing the routing. If the primary router goes |
| difference between IRDP and HSRP. While they have | | | | down, the secondary router quickly takes over with |
| the same basic function, the operation and | | | | no major interruption to network services.The HSRP |
| configuration of each are totally different.The aim of | | | | routers communicate by multicasting updates to |
| both is to allow hosts to quickly discover a standby | | | | 224.0.0.2, and its through these hellos that the HSRP |
| router when the primary router fails. IRDP is | | | | routers decide which router is primary and which is |
| commonly used by Windows DHCP clients and | | | | secondary. HSRP is defined in RFC 2281.The |
| several Unix variations, but you do see it in Cisco | | | | configuration of each of these will be covered in a |
| routers as well. IRDP is defined in RFC 1256.IRDP | | | | future tutorial. In the meantime, I urge you to read |
| routers will multicast Hello messages that host | | | | the RFCs mentioned in this article, and visit to read |
| devices hear. If a host hears from more than one | | | | about the configurations and options available for |
| IRDP router, it will choose one as its primary and will | | | | both of these vital protocols.Chris Bryant, CCIE |
| start using the other router if the primary it's chosen | | | | #12933, is the owner of The Bryant Advantage, |
| goes down.HSRP is a Cisco-proprietary protocol that | | | | home of free CCNP and CCNA tutorials, The Ultimate |
| is designed for quick cutover to a secondary router if | | | | CCNA Study Package, and Ultimate CCNP Study |
| the primary fails, but the host devices don't "see" | | | | Packages.You can also join his RSS feed and visit his |
| either the primary or secondary router. The hosts | | | | blog, which is updated several times daily with new |
| use a virtual router as their default gateway. This | | | | Cisco certification articles, free tutorials, and daily |
| virtual router has its own IP and MAC address! All the | | | | CCNA / CCNP exam questions! Details are on the |
| while, the router chosen as the primary is actually the | | | | website. |