Sample “Best” Summary on Router R2
Figure 21-1 shows four subnets on the right as well as four subnets on the left. So far, this chapter has mostly ignored the subnets on the left, but now you can calculate the best summary route for those subnets. Those routes are for subnets 10.2.1.0/24, 10.2.2.0/24, 10.2.3.0/24, and 10.2.4.0/24.
Figure 21-4 shows the results of the first three steps.
Step 1. Relist the subnet IDs (and prefix lengths) and calculate the subnet broadcast addresses.
Step 2. Identify 10.2.1.0 as the lowest subnet ID and 10.2.4.255 as the highest subnet broadcast address, defining the low and high end of the range that the summary must include.
Step 3. As with the previous example, with all four masks as /24, you choose an initial ...
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