Please fill in the following information:

Issue description

Please do not discuss classful (class-A/B/C) IPv4 networking. 

It has been obsolete for decades, since the introduction of Classless Inter-Domain Routing (CIDR) in RFC 1518 and RFC 1519 in 1993.  You should talk about networks and netmasks, but I would greatly appreciate us removing any references to classful networking.  A historic discussion of this is available in https://datatracker.ietf.org/doc/html/rfc4632 (RFC 4632 / BCP 122), which replaces 1518 and 1519.

Don't confuse classful networking ("class-A networks") with VLSN netmask notation (255.0.0.0 and so on).  VLSN notation is still fine to discuss, although network prefixes might be easier to work with.  Classful networking is not.

In the discussion of IPv4 networks, the following paragraph appears:

In the original IPv4 specification, the allowed network prefixes were one of three fixed sizes for unicast packets that have a single source and destination. The network prefix might be 8 bits (class A), 16 bits (class B), or 24 bits (class C). Today, the number of bits in the network prefix is variable, which means that the prefix can be any number in the supported range, and this later specification
is called Classless Inter-Domain Routing (CIDR). Although fixed-address classes are no longer in use, many network professionals still refer to networks with 8-bit, 16-bit, or 24-bit network prefixes by using the original class A, B, or C designation.

Please cut this entire para. 

I don't want to see the following in the course, but for anyone's education who stumbles on or works on this issue:

Classful networking wasn't just about netmask, it mandated that if you had an address in a particular range, before 1993, you had to use a particular netmask.  In modern notation:

• class-A     0.0.0.0/8 through 127.0.0.0/8, 128 networks except some were reserved.
• class-B     128.0.0.0/16 through 191.255.0.0/16 networks.
• class-C     192.0.0.0/24 through 223.255.255.0/24 networks.

CIDR not only allowed us to use other prefix lengths, but it allowed us to use whatever prefix lengths made sense on whatever subnets we owned that made sense.  So you could have 192.0.0.0/23 and you could have 12.2.3.0/24 and those would be legal.

None of this classful networking stuff has had real meaning (except as legacy stuff while it was phased out) since 1993, it's all legacy from folks using historic terms that don't quite fit how things work now from sheer inertia.  It's all gone now.  See RFC 4632, linked above, for more background.