Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17


In a Private LAN why use variable length subnetmask?

Posted on 2009-03-29
Medium Priority
Last Modified: 2012-05-06
If the recommended number of nodes in a subnet is no more than 512. Why do people mess with the subnetmask to create variable length subnetmasks (private IP's)?

Why not use multiple subnets as below and stick routers in between

With standard subnetmasks you can look at the IP and subnetmask and visually know if two addresses are on the same network. But when using variable length subnetmasks you need to do the working out.

I understand it's useful with public IP's, There must be an advantage in private LANs

Would appreciate someones help

Question by:pancho15
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2

Expert Comment

ID: 24015074
The only real advantage to using VLSM in a network with private IPs would be in route summarization. However: to most network engineers using a /24 subnet for a point to point router connection would bother them on a fundamental level, even if they have the IPs to do it.

Author Comment

ID: 24015234
thanks Sniper,
So your saying you would use a VLSM on the interfaces connecting the routers?

So if you had 10 interfaces connecting routers you would use VLSM to create a suitable IP range ?


Accepted Solution

Sniper98G earned 2000 total points
ID: 24015964
I do.

My network uses primarily Public IPs so I am always very conscious of my IP usage. I have a layer 3 dual core with 14 distribution points all connected to each core using point to point router connections. If I used /24s for all of those I would be wasting 7000 addresses.

Author Closing Comment

ID: 31564120
Thanks you for your help -  makes sense

Featured Post

Moving data to the cloud? Find out if you’re ready

Before moving to the cloud, it is important to carefully define your db needs, plan for the migration & understand prod. environment. This wp explains how to define what you need from a cloud provider, plan for the migration & what putting a cloud solution into practice entails.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Security is one of the biggest concerns when moving and migrating your data from your on-premise location to the Public Cloud.  Where is your data? Who can access it? Will it be safe from accidental deletion?  All of these questions and more are imp…
If you are thinking of adopting cloud services, or just curious as to what ‘the cloud’ can offer then the leader according to Gartner for Infrastructure as a Service (IaaS) is Amazon Web Services (AWS).  When I started using AWS I was completely new…
After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

715 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question