Well of course it didn't "create more", but rather just gives something 
more than classful representation of the old/dumb class a, b, or c 
references of between 254 and 65534 hosts per address assignment for 
subnet sizes in between. There was a reason for the "ip classless" 
command in cisco way back when other devices (and older models) didn't 
understand cidr, or Classless Inter-Domain Routing.

Semantics, yes, it wasn't meant to be an argument, just stating it's an 
evolutionary way of representing mask notations. more than /8, /16, or 
/24 that used to be "good enough" to describe network sizes.  Subnet 
masks are same as cidr, derivative work really represented in decimal 
notations.  Depending what vendor/device you have, it might take subnet 
mask or cidr notation (or both) for various things.

Thanks to microsoft and linksys still teaching the world they needn't 
understand networking, most think 255.255.255.0 is just standard for 
everything when all else fails.

And yes, /31 is a common thing in networking, why waste a /30 with 4 
addresses when you really only need 2 hosts in a network, and there need 
not be a concept of network and broadcast in a point to point link.  
Tastes great, less filling.

https://tools.ietf.org/html/rfc3021

-mb



On 08/31/2015 11:00 PM, Kevin Fries wrote:
>
> I'm not trying to be argumentative, but your logic is misleading.  
> CIDR did not create any more addresses than before CIDR became 
> popular.  If anything it decreased the potential addresses by 
> eliminating the exotic non-linear net masks.  As I said in my previous 
> post... It comes down to the binary.  The binary does not change.  All 
> addresses are binary, all masks are binary, all switching is binary... 
> All built on the work of George Bool, and he rarely gets any credit.  
> CIDR or subnet mask are just two ways of describing the exact same 
> thing.  It's semantics.  Nothing is created or lost in using either 
> form. What you call a /28 used to be referred to as 255.255.255.240, 
> and /30 was 255.255.255.252, and your example of /31 makes no sense at 
> all... This is an unusable network as there are no room for hosts ?!?!?
>
> Kevin
>

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