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best ccna 200-301 book reddit.update messages. In ten microseconds: used by the interface mode configuration command (delay, which sets the default value) and in EIGRP metric calculations. Because of this quirky difference in units, it is important to clarify the units when discussing delay. In particular, in the following example. R1 receives an update for a column with a delay of 100 microseconds, which R1 converts to 10 "ten microsecond" units before using it in the equation. R1 will also see that the S0/1 interface is set to 2000 deciseconds, so for calculation purposes, R1 adds 10 deciseconds, so the total delay is 2010 deciseconds. The result of the metric calculation is shown below.107 metric value = +(10 +2 000) X256 =2 172 416 1544198 Chapter 9 Understanding EIGRP ConceptsHint: IOS will round the result of the division in the formula down to the nearest integer before performing the rest of the calculation. In this example 1()7/1544 is rounded down to to 6476. .If multiple routes to subnet 10.1.3.0/24 exist, then R1 calculates the metric values for all routes and selects the route that has the best (i.e., lowest) metric value to add to the route selection table.Tip: The examples in this chapter show that the default latency setting for routers with Gibbett-class interfaces is 10 microseconds. However, the IOS adjusts the latency based on the actual LAN interface speed. The examples in this and the next chapter have all LAN interfaces at exactly 100 Mbit/s, making the latency 100 microseconds.Bandwidth Warning for Serial LinksThe solid metric that EIGRP has gives it the ability to select routes that contain more router hops, in addition to being able to take advantage of faster links. However, to ensure that the correct routes are selected, administrators must be careful to configure the appropriate bandwidth and default values. In particular, for the example in Figure 9-10, the default bandwidth for the serial link is 1544 and the default latency is 20,000 microseconds. However, IOS cannot automatically change the bandwidth and latency settings based on the rate of the serial link's Layer 1. Therefore, using the default bandwidth and latency in a serial link can create problems.Figure 9-11 shows the problems that arise from using the default bandwidth settings and how EIGRP uses better (faster) routing when the bandwidth is set correctly. The figure focuses on routing B to subnet 10.1.1.0/24 in a variety of scenarios. In the top half of the figure, the default values are used for all serial interfaces, even though the top serial link is only a very slow 64 kbit/s. The bottom half of the figure shows the results when the bandwidth command for the slower serial link is changed to reflect the correct (slow) rate.EIGRP, default broadband EIGRP, correct broadband