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# VLSM calcuation

Posted on 2016-10-31
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Need to subnet 172.16.0.0/16 across 4 regions and support the following nodes

A1 : 510
HQ: 300
A2 255
A3: 168

Any comment for the network ID used in each region, together with the WAN subnet used in each router ? HQ connect to each region in hub-and-spoke network.
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Question by:AXISHK
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Accepted Solution

Miftaul earned 250 total points
ID: 41866739
Are we trying to subnet
Is it an exam question ?
or for production network

A1 - 172.16.0.0/23
HQ - 172.16.2.0/23
A2 - 172.16.4.0/23
A3 - 172.16.6.0/24
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LVL 26

Assisted Solution

Predrag Jovic earned 250 total points
ID: 41867133
Recommendation is to prepare locations to grow. Depending on grow projection you can assign more IP address space to some region then you need to, and then, assign as much IP address space to specific network as it is needed.
The reason for this is simple - easy summarization. You can have only one route for each region.

Example:
Region A1 172.16.0.0/18
Region HQ 172.16.64.0/18
Region  A2 172.16.128.0/18
Region A3 172.16.192.0/18

Then you can start assign IP address ranges for networks in specific region
A1 - network 1 - 172.16.0.0/23
- network 2 - 172.16.2.0/26
- network 3 - 172.16.y.m/z      <----  63 >=y>=0
HQ - network 1 - 172.16.64.0/23
- network 2 - 172.16.66.0/25
- network 3 - 172.16.x.n/z     <----- 127 >=x>=64
etc...

In the case that this was exam question Miftaul gave correct answer - those are smallest IP address ranges for each number of hosts.
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Author Comment

ID: 41867147
This is not on production network.

How about the serial subnet, the network subnet between each region to HQ, should I use
172.16.7.224 / 30
172.16.7.228 / 30
172.16.7.232 / 30

Thx
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LVL 26

Expert Comment

ID: 41867169
172.16.7.x/30 is OK
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Author Closing Comment

ID: 41867875
Thx
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