Exam Essentials

Understand what switching architecture is.  Switches have come a long way in the last few years. From simple systems using shared buses and interrupt-drive access, we have arrived at the crossbar switch-a truly non-blocking architecture suitable for building the largest switches in the busiest environments. But the crossbar is expensive and other mechanisms exist that are suitable for lesser needs. These include the shared memory and distributed shared memory fabrics. And you need to understand how they work, and remember which Cisco switch uses which.

Understand CAM and TCAM.  Storing addressing information in memory is quite easy. The difficult part is referencing it and accessing it quickly. A number of different techniques have emerged in the past to carry out this task, including simple pointing and hash referencing, but all have been slow. A modern, more intelligent process is called a Content Addressable Memory. In the CAM, the location of the data in the memory block is somehow related to the type of data that is stored, making for a much faster lookup.

Even so, the CAM is limited by the fact that there are only two binary numbers, and that means checking every bit. By adding a third bit (the 'don't care' bit) in a mask, the resulting Ternary CAM can provide even faster lookups by ignoring unnecessary bits of information.

Understand switch types. Cisco switches come in a variety of shapes and sizes. As the range changes and becomes more modern, some new switches have appeared. Some of them, such as the fixed-configuration 3550 series, are almost multi-port routers, running native IOS. Others, such as the 4000 and 6500 series, are modular, running updated versions of the IOS. You need to know which switches have which features, and know how to upgrade the CatOS to IOS.

Understand switch management.  Switches need to be managed, and in an increasingly complex network topology, that task also becomes more complex. Cisco has the Cluster Management Suite to help, and there are also a range of show and debug commands that you need to learn, practice, and remember.

CCNP. Building Cisco Multilayer Switched Networks Study Guide (642-811)
CCNP: Building Cisco Multilayer Switched Networks Study Guide (642-811)
ISBN: 078214294X
EAN: 2147483647
Year: 2002
Pages: 174
Authors: Terry Jack

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