Subnets and Supernets

AMD_RULES

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Have a question regarding supernets and subnets. Not quite sure I understand how these work, so I was hoping someone could clarify the concepts. Say I need to design a network to support around 300 devices with these devices being in multiple departments within a company. Since there are more than 254 devices, supernetting would be beneficial, correct? So, if each department is its own subnet would I need to create subnets for these departments and then supernet them? Or is there a way to go straight to supernetting?

As an example:

Dept A - 80 hosts
Dept B - 50 hosts
Dept C - 30 hosts
Dept D - 20 hosts
Dept E - 6 hosts
Dept F - 4 hosts

Thanks!
 

/usr/home

[H]ardness Supreme
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You would use a /23 which supports 510 hosts. Assuming you want all devices in the same subnet/network.
 

firedrow

Limp Gawd
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Are you doing any routing with this? Supernetting is really only used in regards to routing protocols, such as RIP and EIGRP. Internally it's just a bunch of subnets, which I'd suggest using with VLANs. Then either setup a Router-on-a-stick, Layer 3 switch, or your firewall to go between VLANs.
 

Ehren8879

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You could make your life easy and assign equally sized subnets for all sites, all while allowing for growth. For instance a /24 at each site for 253 hosts. Then you're not constantly referring to IPAM or a spreadsheet for netmasks. Plus a /24 is nice, easy to remember netmask.

From a /21 you can carve out eight /24's of which you need six for your existing sites.

Dept A - 80 hosts
Dept B - 50 hosts
Dept C - 30 hosts
Dept D - 20 hosts
Dept E - 6 hosts
Dept F - 4 hosts
 

XOR != OR

[H]ardForum Junkie
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You could make your life easy and assign equally sized subnets for all sites, all while allowing for growth. For instance a /24 at each site for 253 hosts. Then you're not constantly referring to IPAM or a spreadsheet for netmasks. Plus a /24 is nice, easy to remember netmask.

From a /21 you can carve out eight /24's of which you need six for your existing sites.

Dept A - 80 hosts
Dept B - 50 hosts
Dept C - 30 hosts
Dept D - 20 hosts
Dept E - 6 hosts
Dept F - 4 hosts
A /24 leaves a lot of host addresses potentially unused. I think I'd do 6 (8) /25s under a /22 supernet. That'd make the max hosts per subnet 126, which offers plenty of breathing room from 80.
 

Liger88

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You would use a /23 which supports 510 hosts. Assuming you want all devices in the same subnet/network.
I'd probably go a little higher to account for 100% growth.

192.168.0.0 - 192.168.3.255 /22

Dept A - 80 hosts - 192.168.0.1 /24
Dept B - 50 hosts - 192.168.1.0 /25
Dept C - 30 hosts - 192.168.1.128 /26
Dept D - 20 hosts - 192.168.1.192 /26
Dept E - 6 hosts - 192.168.2.0 /27
Dept F - 4 hosts - 192.168.2.32 /27

Gives you a full /24 block to deal with for anything strange and a very flexible 192.168.2.0 subnet to play with just in case while providing enough for growth.

Supernetting is really only done via the router and depending on the size of the business it isn't always necessary for routing purposes (which is its main use to simplify routes).

I'm like XOR in that I believe on maximizing private IP's for good practice, but I'm starting to fall towards the trap of just giving everything a /24 myself lol.
 

AMD_RULES

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So all of the subnets need to be of the same size in a supernet, correct? So it would make the most sense to do all /25 subnets?
 

XOR != OR

[H]ardForum Junkie
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So all of the subnets need to be of the same size in a supernet, correct? So it would make the most sense to do all /25 subnets?
No, they don't. It's usually a good idea ( to keep them the same ) to minimize administrative overhead, but there could be situations where you want to use different subnet sizes.
 

/usr/home

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You could make your life easy and assign equally sized subnets for all sites, all while allowing for growth. For instance a /24 at each site for 253 hosts. Then you're not constantly referring to IPAM or a spreadsheet for netmasks. Plus a /24 is nice, easy to remember netmask.

From a /21 you can carve out eight /24's of which you need six for your existing sites.

Dept A - 80 hosts
Dept B - 50 hosts
Dept C - 30 hosts
Dept D - 20 hosts
Dept E - 6 hosts
Dept F - 4 hosts
This. You could then represent the whole network as a /21.
 

XOR != OR

[H]ardForum Junkie
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So what would a supernet of various size subnets look like as an example?
Same as a supernet with similarly sized subnets.

In order to understand this concept, you need to fully understand what IP addresses are and how subnetting works. After that, it's a simple matter to understand that a supernet is really just a fancy name for a filter to identify interesting and related subnets.
 

AMD_RULES

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I believe I understand how subnets work just not entirely sure I have a grasp on supernets.

Basically, if I divide these departments into subnets of various sizes, I just need to determine an IP address and subnet mask that can represent all of the subnets as one?
 

Liger88

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I believe I understand how subnets work just not entirely sure I have a grasp on supernets.

Basically, if I divide these departments into subnets of various sizes, I just need to determine an IP address and subnet mask that can represent all of the subnets as one?

Exactly. So say you have 4 Departments with a /24 per. That's 1024 IP address spread across 4 x 256 address blocks.

192.168.0.0
192.168.1.0
192.168.2.0
192.168.3.0

To represent all four of them physically (routing as one) and logically (on paper to organize IP addresses across the business) you'd say they belong to the 192.168.0.0 /22 Supernet.

Fully written out that would be 192.168.0.0 255.255.252.0

Each individual subnet would be in 192.168.x.0 255.255.255.0 where X would be 0-3.
 

stormy1

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they give you a /128, which is like... enough IPs to give an IP to every particle in the universe or something....
Actually its a /64 but if they only give you one subnet(/64) you can not properly spit it up without potential issues.
You would have to use ip6 dhcp to do so which is a hack.

The ip6 spec calls for client routers to be assigned a 56(256 x64) but a lot of isps are not doing so.
Comcast you can get more /64s than the standard 1 by using a hint but last I heard they were limiting it to a /60 or 16 x /64 or less in some markets and in others it does not work at all.
 
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AMD_RULES

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Exactly. So say you have 4 Departments with a /24 per. That's 1024 IP address spread across 4 x 256 address blocks.

192.168.0.0
192.168.1.0
192.168.2.0
192.168.3.0

To represent all four of them physically (routing as one) and logically (on paper to organize IP addresses across the business) you'd say they belong to the 192.168.0.0 /22 Supernet.

Fully written out that would be 192.168.0.0 255.255.252.0

Each individual subnet would be in 192.168.x.0 255.255.255.0 where X would be 0-3.
Thank you! :D:D
 
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