Based on the data gathered from the customer's network, the designer should check off any items that are true in the following Network Health Checklist. On a healthy network, it should be possible to check off all the items.
Note that these guidelines are only approximations. Exact thresholds depend on the type of traffic, applications, internetworking devices, topology, and criteria for accepting network performance. As every good engineer knows, the answer to most network performance questions (and most questions in general) is "It depends."
■ No shared Ethernet segments are saturated (no more than 40 percent network utilization).
■ No WAN links are saturated (no more than 70 percent network utilization).
■ The response time is generally less than 100 milliseconds (1 millisecond = 1/1000 of a second; 100 milliseconds = 1/10 of a second).
■ No segments have more than 20 percent broadcasts or multicasts.
■ No segments have more than one cyclic redundancy check error per million bytes of data.
■ On the Ethernet segments, less than 0.1 percent of the packets result in collisions.
■ The Cisco routers are not overutilized (the 5-minute CPU utilization is no more than 75 percent).
■ The number of output queue drops has not exceeded 100 in an hour on any Cisco router.
■ The number of input queue drops has not exceeded 50 in an hour on any Cisco router.
■ The number of buffer misses has not exceeded 25 in an hour on any Cisco router.
■ The number of ignored packets has not exceeded 10 in an hour on any interface on a Cisco router.
The designer should also document any concerns about the existing network's health and its ability to support growth.
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