Book Image

GNS3 Network Simulation Guide

Book Image

GNS3 Network Simulation Guide

Overview of this book

GNS3 is an open-source Graphical Network Simulator used extensively by networking professionals to simulate networking devices such as Cisco, Juniper and Vyatta routers, along with Virtual PCs. GNS3 Network Simulation Guide gives you all the information you need to run a successful GNS3 simulation. You will be guided through the tricky installation pre-requisites and procedures involved in developing a simulated topology suitable for studying for Cisco CCIE Certification. We will also cover many useful tips and tricks which will help you make the most of your GNS3 simulator application. You will begin the GNS3 journey by ensuring that you have prepared your computer with any additional files required by GNS3, to set up the simulated environment needed for a successful installation process. Once GNS3 is installed, you will get to work creating a successful simulation including routers, Ethernet switches, Virtual PCs, and capture packets using Wireshark. Next, you will learn how to master GNS3's Graphical User Interface as well as the Command Console. The inner workings of GNS3 are described in depth so that you gain an appreciation of how UDP tunnels are used to tie the many components of GNS3 together. By following the clear examples and exercises in this guide, you will learn everything that you need to know about how to use GNS3 to prepare for certifications, as well as simulate real-world network scenarios.
Table of Contents (14 chapters)
GNS3 Network Simulation Guide
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

Avoiding the 100 percent CPU utilization problem


Dynamips is an emulator. It takes a binary image designed for a MIPS processor and extracts the machine code commands, just like the MIPS processor would, and tells your computer to execute the equivalent command on your Intel or AMD processor. But many of these instructions will simply be code, to tell the router to wait for something to happen, such as read a packet or send some output to the console. Unfortunately, Dynamips doesn't know which parts of the code it is emulating are the hard working bits, and which bits are the "just hanging around" parts, so it runs them all at full pelt. 100 percent CPU utilization is the result. To prevent this 100 percent CPU utilization, you have to set an Idle-PC value. As Greg Anuzelli (the author of Dynagen) puts it (Anuzelli, Greg. Dynamips / Dynagen Tutorial, http://dynagen.org/tutorial.htm retrieved 5 Feb 2013):

Once [an Idle-PC value] is applied, Dynamips "sleeps" the virtual router occasionally...