alt for @[email protected]Sep 21, 2018

Monday marks a quarter century of classless routing, or CIDR.

25 years since Class A, B, and C addresses were the standard.

On #CIDRDay, saying "class C address" outside a historic/ironic context is a request for enthusiastic wedgies.

Otherwise: cider!

How will you celebrate? #sysadmin #netadmin

Show threadthe Hearth 
@mwlucas Is there any simple way to explain to a non-networking electrical engineer what exactly this means? I'm curious!
Sep 21, 2018 at 5:01pmWeb
Show threadalt for @[email protected]Sep 21, 2018

@Felthry As you're an electrical engineer, so I'll assume you know binary math.

An IPv4 address is a 32-bit number. Under classful routing, you can only divide networks by size on 8 bit boundaries: 8-bit, 16-bit, 24-bit. Most networks are 256 addresses, even if they only need 3 hosts.

With CIDR, you can divide networks on any bit you like.

Show threadthe Hearth Sep 21, 2018
@mwlucas That makes sense. Well, it doesn't make sense why they would design it that way but I guess they probably had a reason.
Show threadalt for @[email protected]Sep 21, 2018
@Felthry The reason's easy. "The Internet's never going to go anywhere. We'll never have more than, say, three hundred hosts on it."
Show threadalt for @[email protected]Sep 21, 2018
@Felthry there's a decent explanation at https://www.digitalocean.com/community/tutorials/understanding-ip-addresses-subnets-and-cidr-notation-for-networking, or I have a writeup in "Networking for Systems Administrators," https://mwl.io/nonfiction/networking#n4sa
Understanding IP Addresses, Subnets, and CIDR Notation for Networking | DigitalOcean

IP addresses, networks, submasks, and CIDR notation can be difficult concepts to understand. In this guide, we will cover some of the basic ideas behind how these systems work together to allow computers to communicate over the internet.