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