Scenario 1Bad Subnetting

Scenario 1”Bad Subnetting

In Figure C.1, you will see a hub and spoke network. There are two subnetted IP addresses. One address is there to throw you off and is invalid. Do you know subnetting well enough to tell which link has an invalid subnet?

Figure C.1. A diagram showing invalid subnetting.

The link between Atlanta and Denver would be the problem link. The reason is that a /27 network is the same as stating a subnet of 255.255.255.224 . If you take a magic number of 256 and subtract 224 , you get 32 . This means that the first network would be the .32 network, then second the .64 network. The broadcast addresses in the .32 network would be .63 and all the addresses in between would be valid. This means that if the interface in Denver was 172.16.1.33 , the only valid addresses in that network would be from .34 to .62 . Only those addresses could be used on the Atlanta side of the link.