Routing Switch Applications

From the perspective discussed in the previous paragraphs, it becomes clear that MLS is most comfortable in a more Layer 2-oriented world. Although its Layer 3 performance is very respectable, this is not what sets MLS apart from the 8500s. What does differentiate MLS is its capability to very tightly integrate Layer 2 and Layer 3 processing.

For example, designs utilizing campus-wide VLANs can benefit greatly from MLS support. Although Chapter 14 argues that campus-wide VLANs are not the best approach for most networks, they can be very effective in certain situations (for example, when specific user mobility and security issues exist). Given the router-oriented nature of the 8500s, it can be tedious to mix Layer 2 and Layer 3 processing in more than the simplest configurations (this point is discussed in more detail in the section on Integrated Routing and Bridging [IRB] at the end of the chapter).

Designs utilizing a more hierarchical approach (such as the "multilayer model" discussed in Chapter 14) can also benefit from MLS. Not only can it be used to implement the Layer 3 switching component required by this design, it can do it with considerable flexibility. One case where this flexibility can be advantageous is where the user requirements are such that you would like to have VLANs (in other words, IP subnets and IPX networks) that traverse multiple MDF switches in order to reach multiple IDF switches. For example, both a user connected to IDF-1 and another user connected to IDF-2 could be placed in the "Marketing" VLAN and have IP addresses on the same subnet.

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