Solved

Subnet a subnet

Posted on 2014-10-19
5
361 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
Comment Utility
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
Comment Utility
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
Comment Utility
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
Comment Utility
Thank you! This is topclass educating answer and I will have it in my Q&A
0
 
LVL 18

Expert Comment

by:Akinsd
Comment Utility
Thanks for the kind words

All the best
0

Featured Post

Highfive + Dolby Voice = No More Audio Complaints!

Poor audio quality is one of the top reasons people don’t use video conferencing. Get the crispest, clearest audio powered by Dolby Voice in every meeting. Highfive and Dolby Voice deliver the best video conferencing and audio experience for every meeting and every room.

Join & Write a Comment

Suggested Solutions

Title # Comments Views Activity
Joining Domain Issue 4 31
Route all internet traffic through this VPN (sonicwall) 2 31
OSPF Design NSSA 5 30
HSRP needed? 4 25
Network ports are the threads that hold network communication together. They are an essential part of networking that can be easily ignore or misunderstood, my goals is to show those who don't have a strong network foundation how network ports opera…
Don’t let your business fall victim to the coming apocalypse – use our Survival Guide for the Fax Apocalypse to identify the risks and signs of zombie fax activities at your business.
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…
This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg). If you're looking for how to monitor bandwidth using netflow or packet s…

771 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

Need Help in Real-Time?

Connect with top rated Experts

10 Experts available now in Live!

Get 1:1 Help Now