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I'm new to networking and am trying to get my terminology straight. I've Google this question but haven't found anything that clearly explains it.

  • Can you add a bit more information about what exactly you are not sure about? I have never come across the term "netblock". – Mark Riddell Aug 25 '16 at 19:06
  • @MarkoPolo Have you tried googling it? I think its shorthand for network block. – Nathan Aug 25 '16 at 19:32
  • Yes I Googled it and there are very few references to the term. Definitely not a common term which is why I was curious about context. – Mark Riddell Aug 25 '16 at 19:33
  • Is network block more common? – Nathan Aug 25 '16 at 19:34
  • In what context? What are you trying to describe? – Mark Riddell Aug 25 '16 at 19:35
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I'm not sure that there is an official definition of "netblock", but in common usage, I've most frequently heard it used in reference to an IP address allocation assigned by an RIR to another organization.

"Subnet", on the other hand, is a more broad networking concept, used when referring to a portion of the IP addresses that are part of a larger network scope.

So, to use these terms together, I will use this fictitious situation:

  • ARIN has allocated the 203.0.113.0/24 netblock to MyBigCorporation
  • MyBigCorporation needs to subdivide this allocation into smaller subnets for various purposes, so...
  • MyBigCorporation allocates 203.0.113.0/28 (a subnet of 203.0.113.0/24) for use by their inbound MXes
  • This is as I understand it in a MSO context. – Andrew B Aug 25 '16 at 19:39
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A word about the word subnet:

The word subnet is, IMO, incorrectly used most of the time from a purely technical definition. What people generally refer to as a subnet is actually just a network. A subnet is when you take a network and divide it into smaller networks, hence subnetworks, or subnets.

If my internal company network is 10.1.0.0/16 then that is my network, it is not a subnet. If I break that 10.1.0.0/16 network into smaller /24 networks then I have created subnets from that network.

If I have a 10.1.0.0/16 network and a 10.2.0.0/16 network then I have two networks, not two subnets. A subnet is a logical division of an IP network.

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