VLSM offers the ability to use variable length subnet masks in an enterprise environment with the primary purpose of conserving address space. As seen in the exhibit we have three routers with two WAN segments – both configured with a 30 bit subnet mask which is appropriate for links between routers.
We also have three Ethernet networks configured, each with variable size subnets.
Overall there are two failures with this network. It simply will not work. As a certified Cisco® CCNA candidate can you identify the problem? If you can, that is excellent. If not, do you have plans for tackling the subnetting portion of the Cisco CCNA exam? It can be real tough if you are not prepared.
Keep in mind that a network design like this will require the use of a protocol that will support VLSM, and the use of a Summary Route and all routing protocols will not.
As with the original Subnetting Made Easy, these additional tasks may be covered in a day or so. Keep in mind though; you will need to keep practicing. Just like playing guitar, you can’t quit practicing and expect to be sharp!
Our revised Subnetting-Made-Easy study guide has been released February 2010, addresses the newer Cisco® CCNA (640-802) test objectives and will help make this portion of the exam a breeze.