I am starting my studies in networking and starting off with the basics of IP addressing and Subnetting with CIDR values.
My Question here is 1st how can you tell the subnet class of an IP address just from the 1st Octet such as 172.0.0.0 & 192.0.0.0
from my understanding a 0.0.0.0 – 127.255.255.255 is a Class A, 128.0.0.0 – 191.255.255.255 is a Class B, 192.0.0.0 – 223.255.255.255 is Class C.
But from following this Vid channel:- https://www.youtube.com/channel/UCnRCUB8utEFY0xqm7L92yZg
i have learnt that the /28 at the end of an IP address is the CIDR Value which is the total number of bits used in subnetting so a /28 will be 8.8.8.4 or 255.255.255.240 `
is IP address of 172.168.10/28 a Class B or Class C
My Confusion comes from above where 128.0.0.0 – 191.255.255.255 IP range is a Class B but the /28 means 8.8.8.4 = 28 Bits for the network which leaves us with only 4 bits for Hosts as a Class C Subnet is 8.8.8.0 or 255.255.255.0.
So is IP address of 172.168.10/28 a Class B or Class C?
Please, can somebody clarify this for me.
Thanks in advance
Best Answer
First, network classes are dead, killed in 1993 by RFCs 1517, 1518, and 1519, which defined CIDR (Classless Inter-Domain Routing). Later RFCs have further deprecated network classes. Modern networking doesn't use network classes, and you should only worry about them from a historical perspective.
IPv4 network classes were defined by the first few bits of the address, and IPv6 never had network classes. The latest RFC of which I know that defines network classes is RFC 1166, Internet Numbers*, which obsoleted the previous RFCs for network classes.
The network classes had specific mask lengths, but could be subnetted to longer mask lengths within a specific classful network. Unfortunately, many people confuse the network mask with the network class, and many of them will argue to the death that any
/24
network is a Class C network, but that is not the definition of a network class.Actually, neither. The address
172.168.10/28
is actually an invalid IPv4 address. I will assume you meant172.168.10.0/28
, which used to be a subnet of the172.168.0.0/16
Class B network.Today, trying to classify an address by network class is a pointless exercise because there is no longer any such thing.
*Copied from the RFC.