Subnetting Clarification

Routing & Switching
1

I have a few questions around subnetting:

  • My understanding is that networks were broken into classes. This was inefficient. So CIDR was released to allow for “subnet” bits to be browed from the host and additional networks to be created. Is my understanding correct?
  • When subnetting do we always start from the default mask. i.e for a Class A network do I always start with a /8 and then subnet from there?
  • VLSM then allowed for these subnetworks to be variable in length rather then all being the same size. Is my understanding correct?
  • One confusion I have is around RFC1918, the RFC states:

10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

However, online there seems to be a mix of what the subnet mask should be. Some sites say it should be /8, /12, /16. But on this site, the examples are based on /8, /16, /24.

Thanks,

2

A post was merged into an existing topic: What is Subnetting?