Class C VLSM Assistant

When working with Class C addresses, you have a maximum of 254 host addresses that you can use. When you need to share the host addresses across multiple subnets, the task of assigning addresses becomes more complex. Using a routing protocol (ie RIP, IGRP) that does not support variable length subnet masks (VLSM) wastes valuable host addresses. VLSM maximises the number of host addresses that can be used . To use the results from this Assistant, you must use a routing protocol that supports VLSM (ie OSPF, EIGRP, RIP V2, etc).

The new Class C VLSM Assistant will calculate variable length subnet masks and host address ranges for up to 30 subnets each with a differnet number of hosts.

The Assistant will initially prompt you for your Class C network address. Next it will ask you for the number of subnets you want the assistant to calculate masks and address ranges for. Finally, you are required to enter the number of hosts in each subnet. The Assistant will then calculate the address ranges and Variable length subnet mask for each subnet. If a given subnet cannot be accomodated in this calculation, it will be flaggd accordingly.

The Assistant gives preference to subnets with larger numbers of hosts. These subnets will be assigned address ranges before subnets with a smaller number of hosts. An example of the output from the report is displayed below:

  TCP/IP Network Assistant V3.11 © 1996 - Carl Solder
  Results of Class C VLSM Assistant are:
  Number of segments chosen is 7
  Segment 1 has 43 hosts
  Segment 2 has 34 hosts
  Segment 3 has 25 hosts
  Segment 4 has 22 hosts
  Segment 5 has 12 hosts
  Segment 6 has 2 hosts
  Segment 7 has 2 hosts
  Subnet 1 lower address is 200.1.1.129
  Subnet 1 upper address is 200.1.1.190
  Subnet mask for segment 1 is 255.255.255.192
  Subnet 2 lower address is 200.1.1.65
  Subnet 2 upper address is 200.1.1.126
  Subnet mask for segment 2 is 255.255.255.192
  Subnet 3 lower address is 200.1.1.193
  Subnet 3 upper address is 200.1.1.222
  Subnet mask for segment 3 is 255.255.255.224
  Subnet 4 lower address is 200.1.1.33
  Subnet 4 upper address is 200.1.1.62
  Subnet mask for segment 4 is 255.255.255.224
  Subnet 5 lower address is 200.1.1.225
  Subnet 5 upper address is 200.1.1.238
  Subnet mask for segment 5 is 255.255.255.240
  Subnet 6 lower address is 200.1.1.29
  Subnet 6 upper address is 200.1.1.30
  Subnet mask for segment 6 is 255.255.255.252
  Subnet 7 lower address is 200.1.1.25
  Subnet 7 upper address is 200.1.1.26
  Subnet mask for segment 7 is 255.255.255.252

Last Modified: 12 August 1996 - Carl Solder