GNS3 is a famous network simulator which allow to test network topologies and equipements.
Installation
First you have to install Telnet and PyQt4 library with :
natjohan# yum install telnet pyqt4
Then, install GNS3, download the tgz archive from the official website :
natjohan# tar -xvzf GNS3-0.8.3.1-src.tar.gz ...