Performace Issues Based On Large Subnet

This should be a fairly easy, opinion based question.  When designing a private network segment (NATed), what would be the pro’s and con’s to using a Class B IP network vs a Class C.  Biggest question in the pro’s and con’s is can anyone see network performance deteriorating because a Class B was used rather than a Class C.   The idea behind the Class B is to us the third octet to designate functionality in the network, for example 10.1.0.x is where routers/switches/firewall’s go, 10.1.1.x is where the Servers go, 10.1.2.x where the phones go, and so on.  Does anyone see an performance issue with this?
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          There would be no performance issues with using a mask for this. The only potential drawback you would have would be if you were trying not to waste IP addresses because this subnet will consume 65,535 addresses. If you are worried about consuming too many addresses you can use VLSM to create smaller subnets and save address space. For example you can make your subnet mask to break your subnet to use up to 32 blocks of 2048 addresses.

Best of luck,
I dont see any performance issues as long as you dont add too many clients to a subnet. 50-100 per subnet on a 100mbit network should be fine, as long as they are not doing to much ... if the clients are hogging the network, you want to lower that... this is where you create a baseline... as far as A vs B vs C.... most businesses use 10.x.x.x vs a 192...
Keith AlabasterEnterprise ArchitectCommented:
If you use the Class C mask, something is going to have to perform the routing between the subnets; using a class B removes that overhead. using a class B increases the broadcast traffic as they are now all on the same subnet. Personally I would use the class C mask and live with the router device having to earn its keep.
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Technically, the right answer is the answer of needs and advantages in fitting into future situations and the need not to totally re-engineer a concept to resolve a standing issue.  You want to save money by not reinventing how you think about your network.  

Would it be more economical to have a subnetwork which can contain a possibility of 65,534 devices; stand that network up and having laid everything down, then proceed to subdivide when the need arises.  What work processes will that break?

Or allocate a subnetwork which can house a potential of 254 devices and add on subnetworks as your topology grows.  As every subnet is contained, this modular approach of adding is less painful than dividing.

In terms of size of the subnet; dividing by the last octet is probably the most common practice and would be most recommenable.  Unless you like or need to divide otherwise.

The largest site I've ever seen has not exceeded 3,000 addressable devices and the ip address structuring was laid out in such a manner that accomodated growth per floor, number of buildings and quadrant of the campus.  They generically used the 10's private subnet, the 2nd octet IDed the building, the 3rd octet IDed the floor per the building and the last octet IDed the individual devices per the floor.  There was considerable growth potential built into this scheme in all directions.

In terms of layer 2 broadcast, you definitely want to have a small footprint, however you go.


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Was that really you Tim?


Well put!

IM trying to think like THAT... :))


Keith AlabasterEnterprise ArchitectCommented:
Thanks for the confirmation Tim.
Hi Craig,

What's JK?


just kiddin!
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