The tool is not as full featured

Sem Sim also offers 6 different practical router simulation scenarios to help gauge your knowledge and proficiency in with routing concepts. A test mode is available that provides  MapleStory Gold a skill assessment, and a detailed study plan to speed up sudy times and improve test scores. Additionally, Sem Sim gives you 70 plus flash card based CCNA practice questions that help build your knowledge of the IOS commands.V-LabV-Lab offers a free online router lab simulation tool.

The tool is not as full featured as some others but it is free. Additionally you will need to schedule lab time, so access is not always available. V- Lab does however offer several great resources for learning including several very well documented scenarios. V-Lab is certainly worth a try just to get a feel for working in the IOS and learning some basic commands.Sybex CCNA Virtual Lab, Titanium EditionIf you want a more structured lab experience, Sybex's CCNA Virtual Lab, Titanium Edition is your tool. The book and software combination provides users with a tool that can create a simulated lab of up to four switches, three routers, and six hosts. The book contains a very thorough list of exercises to follow or you can just experiment with the lab.

The virtual lab offers access configuration consoles for network devices, including Cisco routers 2621,1900, 2950, and 3550 Cisco switches, and boasts an impressive 470 Cisco commands. There is also a great tool for testing your newly acquired skills called Net Assessment. Net Assessment, a tool for generating and evaluating problem-solving scenarios can create scenarios for you to troubleshoot.NetSim - Network Simulation SoftwareBoson offers a router more information at link: http://www.mmomesos.com/