TAILIEUCHUNG - CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 34

Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 34 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | I Page 299 Tuesday May 20 2003 2 53 PM Collision Domains and Broadcast Domains 299 Table 5-7 lists the average number of broadcast and multicasts for IP networks. Table 5-7 Average Number of Broadcast and Multicasts for IP Networks Number of Hosts Average Percentage of CPU Loss Per Host 100 1000 10 000 Although the numbers in Table 5-7 might appear low they represent an average well-designed IP network that is not running the Routing Information Protocol RIP . When broadcast and multicast traffic peak because of storm behavior peak CPU loss can be orders of magnitude greater than average. Broadcast storms can be caused by a device requesting information from a network that has grown too large. So many responses are sent to the original request that the device cannot process them or the first request triggers similar requests from other devices that effectively block normal traffic flow on the network. An IP router is a router or workstation that runs any distance vector routing protocol. Some administrators configure all workstations to run RIP a routing protocol as a redundancy and reachability policy. Every 30 seconds RIP uses broadcasts to retransmit the entire RIP routing table to other RIP routers. If a large number of routers were configured to run RIP and on average 50 packets were required to transmit the routing table the routers would generate 3333 broadcasts per second. Most network administrators configure only a small number of routers usually five to ten to run RIP. For a routing table that has a size of 50 packets 10 RIP routers would generate about 16 broadcasts per second. Routing protocols and routing table are discussed in Chapter 8 Routing Fundamentals and Subnets. IP multicast applications adversely can affect the performance of large scaled switched networks. Although multicasting is an efficient way to send a stream of multimedia data to many users on a shared-media hub it affects every user on a flat-switched .

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