Solved

Subnet a subnet

Posted on 2014-10-19
5
365 Views
Last Modified: 2014-10-25
We have a MPLS network our ISP provides us with. It is a /20 network.
Now we want to have several vlans but we don't want to tell our ISP every time we need a vlan so we want to create all our vlans on our Layer 3 switch.

Our ISP tells me they will on their router point the entire /20 network to our Layer 3 switch. And so we can subnet the /20 network the into the subnets we like.

So I guess as long as I subnet using  /21 /22 /23 /24 this is possible?
0
Comment
Question by:Bes4dmin
  • 2
  • 2
5 Comments
 
LVL 24

Expert Comment

by:Ken Boone
ID: 40390889
Yes that is correct.  If you have one connection on the MPLS network that the provider is routing a /20 to .. you can chop that up however you see fit at that location.  

Now if you have 8 MPLS locations and the /20 is already chopped up between all locations that is a different story.  But it sounds like they are routing a /20 down a single network connection to a single location.
0
 
LVL 1

Author Comment

by:Bes4dmin
ID: 40390906
we have six MPLS locations and each one of them have a /20 address. E.g one site has  172.16.80.0/20 and the other has 172.16.96.0/20
So every site can take after us then and start subneting. :-)
0
 
LVL 18

Accepted Solution

by:
Akinsd earned 500 total points
ID: 40391383
Let's categorize the ranges given to you are supernets, and we need subnets within each supernet

Supernet 1 (Site1) = 172.16.80.0 /20 means you can have addresses between 172.16.80.1 - 172.16.95.254, but Actual range = (172.16.80.0 - 172.16.95.255)
Supernet 2 (Site2) = 172.16.96.0 /20 means you can have addresses between 172.16.96.1 - 172.16.111.254 but Actual range = (172.16.96.0 - 172.16.111.255)
Site 3  range = 172.16.112.0 - 172.16.127.255
Site 4 range = 172.16.128.0 - 172.16.143.255
Site 5 range = 172.16.144.0 - 172.16.159.255
Site 6 range = 172.16.160.0 - 172.16.175.255

Both of these gives you 4,094 hosts each
The standard recommendation is a maximum 510 hosts per subnet for optimum performance anyways (Speed, congestion and collision are important factors).

What you'll nee to do is Subnetting. To do these, you will use notations greater than the one your ISP gave you, eg /21, /22, /23, /24, /25, /26, /27, /28, /29, /30, but you must still confine the address within the range you were given eg, Supernet 1 = minimum subnetted address - 172.16.80.1; Max - 172.16.95.254

Let's assume you plan to have about 500 hosts in your network, you will use /23 (255.255.254.0) which gives you 510 hosts
So your first assignable address in subnet 1 = 172.16.80.1 /23. Last assignable  Address = 172.16.81.254 /23
subnet 2 = 172.16.82.1 /23 - 172.16.83.254 /23
This continues up to subnet 8 = 172.16.94.1 /23 - 172.16.95.254 /23

If you think 1 subnet would not need more than 254 addresses, then you can use a /24 notation. This will give you up to 16 subnets within your supernet.
first assignable address in subnet 1 = 172.16.80.1 /24. Last assignable  Address = 172.16.80.254 /24
up to subnet 16 = 172.16.95.1 /24. Last assignable  Address = 172.16.95.254 /24

/23 (255.255.254.0)
Site 1                                          Site 2
172.16.80.1 - 172.16.81.255      172.16.96.1 - 172.16.97.255
172.16.82.1 - 172.16.83.255      172.16.98.1 - 172.16.99.255
172.16.84.1 - 172.16.85.255      172.16.100.1 - 172.16.101.255
172.16.86.1 - 172.16.87.255      172.16.102.1 - 172.16.103.255
172.16.88.1 - 172.16.89.255      172.16.104.1 - 172.16.105.255
172.16.90.1 - 172.16.91.255      172.16.106.1 - 172.16.107.255
172.16.92.1 - 172.16.93.255      172.16.108.1 - 172.16.109.255
172.16.94.1 - 172.16.95.255      172.16.110.1 - 172.16.111.255


/24 (255.255.255.0)
Site 1
172.16.80.1 - 172.16.80.255
172.16.81.1 - 172.16.81.255
172.16.82.1 - 172.16.82.255
172.16.83.1 - 172.16.83.255
172.16.84.1 - 172.16.84.255
172.16.85.1 - 172.16.85.255
172.16.86.1 - 172.16.86.255
172.16.87.1 - 172.16.87.255
172.16.88.1 - 172.16.88.255
172.16.89.1 - 172.16.89.255
172.16.90.1 - 172.16.90.255
172.16.91.1 - 172.16.91.255
172.16.92.1 - 172.16.92.255
172.16.93.1 - 172.16.93.255
172.16.94.1 - 172.16.94.255
172.16.95.1 - 172.16.95.255

Bottom line, 2 key factors
How many subnets do you desire in each supernet
How many host do you desire per subnet

In my examples above,
/23 will give you 8 subnets and 510 hosts per subnet.
/24 will give you 16 subnets and 254 hosts per subnet

I think you get the logic
subnets double while hosts breaks in halves as you go up the notation ladder


I hope this helps
0
 
LVL 1

Author Closing Comment

by:Bes4dmin
ID: 40391596
Thank you! This is topclass educating answer and I will have it in my Q&A
0
 
LVL 18

Expert Comment

by:Akinsd
ID: 40404367
Thanks for the kind words

All the best
0

Featured Post

Efficient way to get backups off site to Azure

This user guide provides instructions on how to deploy and configure both a StoneFly Scale Out NAS Enterprise Cloud Drive virtual machine and Veeam Cloud Connect in the Microsoft Azure Cloud.

Question has a verified solution.

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

Suggested Solutions

If your business is like most, chances are you still need to maintain a fax infrastructure for your staff. It’s hard to believe that a communication technology that was thriving in the mid-80s could still be an essential part of your team’s modern I…
ADCs have gained traction within the last decade, largely due to increased demand for legacy load balancing appliances to handle more advanced application delivery requirements and improve application performance.
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), 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…
Here's a very brief overview of the methods PRTG Network Monitor (https://www.paessler.com/prtg) offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…

809 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