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this document for mercial distribution and exclusive use by instructors in NA 3:
Switching Basics and Intermediate Routing course as part of an official working Academy
Program.
Lab Calculating VLSM s
Objective
Use variable-length mask (VLSM) to support more efficient use of the assigned IP addresses
and to reduce the amount of routing information at the top level.
The solution to this VLSM lab is provided in the steps themselves. Students should take the
mended ting in each step and build a diagram of work, showing routers, LANs
and WAN links. Each LAN and WAN link should be labeled with the appropriate address and
slash number. A suggested diagram can be found at the end of this lab.
Background/Preparation
A class C address of has been allocated.
Perth, Sydney, and Singapore have a WAN connection to Kuala Lumpur.
• Perth requires 60 hosts.
• Kuala Lumpur requires 28 hosts.
• Sydney and Singapore each require 12 hosts.
To calculate VLSM s and the respective hosts allocate the largest requirements first from the
address range. Requirements levels should be listed from the largest to the smallest.
In this example Perth requires 60 hosts. Use 6 bits since 26 – 2 = 62 usable host addresses. Thus 2
bits will be used from the 4th octet to represent the work-prefix of /26 and the remaining
6 bits will be used for host addresses.
1 - NA 3: Switching Basics and Intermediate Routing v - Lab Copyright 2003, Cisco Systems, Inc.
Step 1
The first step in the ting process is to divide the allocated address of into four
equal size address blocks. Since 4 = 22, 2 bits are required to identify each of the 4 s.
Next, take #0 () and identify each of its hosts.
Allocated Address works 62 usable hosts/work ( #0)
1