Are Cisco admins expected to understand classful networks?
While studying for the CCENT exam, my reference materials have made an alarming number of references to class A/B/C networks. Thankfully they just treat Class A/B/C as shorthand for /8, /16, and /24 CIDR subnets, and don't make any mention of an implicit subnet from the first nibble. Still, it throws me off to have "Class B" pop up in a question or explanation and have to remind myself at every step that there is an implied /16 mask in there.
Is this a convention that is still widely used despite being obsoleted over two decades ago? Am I going to just have to get used to this from my senior admins? And, perhaps most importantly, does Cisco expect its certified technicians/associates/experts to accept and use classful network terminology? (Ignore the last question if it violates Cisco's exam confidentiality policy.)
Update: After switching to a more authoritative reference/study guide, it became clear that Cisco expects knowledge of actual classful networks, insofar as the official study guide dedicates several chapters to them. This makes the question less about the A/B/C terminology and more about if/why admins are expected to know about classful networks.
Solution 1:
You should know three things about class-based-routing:
Class-based routing was a simpler system that was abandoned (in 1993) long before most people ever heard about the Internet. In all likelihood, nobody you will ever know has used it. And if any of your network equipment is that old, you should seriously consider alternate employment. The system used the first few bits of the address to determine its class, and (indirectly) its netmask. Note that the netmask was implied in the class, it did not determine the class. Saying you have a "Class C at 172.16.1.0" will earn you a swift kick from anyone with even a vague understanding of class-based routing.
People currently say Class A, B, and C to mean /8, /16, and /24 netmasks, respectively. As should be obvious from the above, they do so incorrectly. They typically think it makes them appear knowledgeable and wise to the history of of the Internet (oh, the irony).
Some hold-overs of the original system still exist. "Class D" (prefix 224 to 239) is still multicast, and "Class E" (prefix 240 to 255) is still "Reserved" or "Experimental". Plus, some (older) systems assume a default netmask based on the original class designation; so /8 for prefix 0 through 128, for example. This is often more annoying than helpful, but that's where it came from.
Solution 2:
The only people I have ever met who use the terms "Class A/B/C" are people who are using them incorrectly to mean a /8 or a /16 etc (except for just one person who used "Class A" to be the first octet, "Class B" to be the second octet, etc. But he was an idiot who refused to change his phrasing even though it led to so much confusion).
So go ahead and learn about classful addressing. More knowledge is better. But the most important thing to learn about "Class A/B/C" addresses is:
- You should never actually use those terms
- When you hear someone else using those terms, they are using them incorrectly
It's a good way of telling who actually knows their stuff and is experienced outside of theory. It would throw up red flags if I heard the terms used incorrectly in a job interview.
Solution 3:
In a word, yes.
People will often talk about it in the same way that the course material does. Nobody uses classful networking, or at least nobody I've encountered; during infrastructure/architecture planning people will often say things like "we'll set them up with two class C's here." It's easier than saying "we'll give them a /23" or "172.16.0.0-172.16.1.254 should be enough" and it communicates the same message.
While it may not be technically 100% accurate, lots of the stuff that gets thrown around in industry conversation isn't to spec, eg: router/switch/AP\Bridges aren't referred to as anything other than routers.
Regarding the second question, I don't think it violates, but you're expected to understand the exam topics as it's presented in the material reading. That is, you need to know what they are, and you need to understand that they often refer to those specific subnets.