Do I Need to Understand VLSM to Pass the CCNA Certification Exam?

Today I received the following email from a former student:

"Hi,
I was in your Fall CCNA class and I am preparing to take the CCNA exam and have been following the notes I have from your class, CBT nuggets video, your sild you gave us. I have been doing simulations on different topologies/protocols like Rip/version 2, OSPF, EIGRP and IS IS.

I will like to know do I need to worry much about VLSM? I have been practicing doing basic subneting off the top of my head ???"

My response to this student:
You, as an IT professional, need to understand the concept of VLSM and how to apply it to a network. As you learned in class, the benefits of VLSM is more efficient utilization of available address space and reduced size of route advertisements. Any company IT department will expect you, as a CCNA, to understand and implement VLSM – regardless of whether it was on the actual exam or not.

As an example, let’s assume you were given a single class C IP address of 193.160.1.0/24 from your upstream provider. From that, you need to create four subnets – one for payroll (30 hosts), one for marketing (12 hosts), one for administrators (60 hosts), and one for clerical staff (100 hosts) – all different sizes.

Without VLSM, each subnet would need to accommodate 100 hosts which would not be possible with that class C address you were given. The clerical staff, alone, would use up half of your address space leaving you one subnet! For example: 193.160.1.0/25.

With VLSM, we would be able to accommodate all four workgroups. We would be able to use VLSM to subnet that second block of address space (192.160.1.128/25).

The results: Clerical Staff – 193.160.1.0/25 with 100 hosts; Administrators – 193.160.1.128/26 with 60 hosts; Payroll – 193.160.1.192/27 with 30 hosts; and Marketing – 193.160.1.224/28 with 12 hosts.

If you understand what I have described, you should do just fine with VLSM on your CCNA cert exam. If not, make an appointment to see me so we can get it down cold.

Hope this helps!