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CCNA® Cisco Certified Network Associate: Study Guide, Seventh Edition by Todd Lammle

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Variable Length Subnet Masks (VLSMs)

In this chapter I’m going to show you a simple way to take one network and create many networks using subnet masks of different lengths on different types of network designs. This is called VLSM networking, and it does bring up another subject I mentioned in Chapter 4: classful and classless networking.

Neither RIPv1 nor IGRP routing protocols have a field for subnet information, so the subnet information gets dropped. What this means is that if a router running RIP has a subnet mask of a certain value, it assumes that all interfaces within the classful address space have the same subnet mask. This is called classful routing, and RIP and IGRP are both considered classful routing protocols. (I’ll be talking ...

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