subnet masks

There was subnetting long before the classless rules were established. Check out basic subnetting on this site. Also it helps to know some of the history of networking to fully comprehend the present.

The history lesson is much to extensive for this forum. However, to try to make a long story short when network classes were made so were routing protocols and subnetting rules. When a subnet mask is placed on an interface a classful routing protocol can recognize this. However subnet masks are not sent in routing updates so subnets are assumed partially due to interface configurations. This changed with new classless routing protocols as subnet information is sent in the routing updates of classless routing protocols.

When it was recognized that we were fast running out of IP addresses due to the rapid expansion of the internet and that using classful routing protocols caused a great waste of ip addresses it was determined that we could reduce that waste by changing the rules. This is what was done as a temporary fix to help create the time needed to establish the rules for IPV6.

This temporary fix worked so well that while IPV6 has been with us for some time now yet it’s implementation is still only in the beginning stages.

What is important to understand is it that it is not so much that addresses are classful or classless but dynamic routing protocols are either classful or classless. Fully understanding the operation of these protocols helps in understanding the difference between classful and classless.

RIP and IGRP are classful. RIP version 2, EIGRP, OSPF, and IS-IS are all classless routing protocols. Classful and classless routing protocols operate under there own set of rules and as might be guessed each protocol has it’s own set of advantages/disadvantages and uses.

Not everyone can afford or have the time to go to courses such as Cisco Academy, or even afford the books that you reference. Even if you go through a course or read a book doesn't mean you'll necessarily comprehend every last detail. I had a misconception about VLANs for a long time that Chris was able to correct in a polite manner. Everyone needs a mentor that can help them along with the small parts that they missed in their studies.

People should be able to post their questions and opinions of networking without regards of whether it is correct or not. If everyone was right and knew the entire history of networking, then this message board would not be needed. There are many questions I see on this board that can be answered with a quick Google, but for many, they need a human response to confirm their questions.

I've been monitoring this discussion with much interest and think its time I deposit my 2 cents worth!

I'm my opinion, Mew is correct regarding the Classful and Classless Subnetting concepts and routing protocols. A quick visit (as he suggested) to the appropriate topic [ www.firewall.cx/ip-subnetting-mask-effect.php ] will show that the topic is covered and confirmed on this site aswell, and since Cisco link to us in their CCNA academy program... well we can assume its correct

On the other hand, Jwj is also correct about the expensive books and courses which a lot of people cannot unfortunately afford to purchase or attend, and we are doing something about this (I'm sure jwj will agree with me!). Our recent news about the free book give-aways we've managed to get from the world's leading publishing companies (check home page news announcement or Cisco Lab forum) will help our 'small' community benefit and not suffer from these problems. The Cisco lab will also come in place to cover the hands-on experience the lucky CCNA Academy students get, so we'll try and give everyone the best of both worlds


We are all here to benefit from each others knowledge and experience so there is no need to be nice to each other - ops .. Sorry about that ....I meant, we should try and be nice to each other

Cheers people !

Hey Chris how’s it going . I know you and I share a common interest in subnetting . I was actually surprised not to see a post from you sooner on this subject . First let me say that to me a correct answer to a question is important. I seldom give an opinion though I obviously must give a little attitude or I would not get the comments I get now and again :oops: . My answers are researched and I’m sorry if sometimes I get a little short with those that are quick to question my comments rather than do a little research themselves .

I also understand the constraints that might prevent some from pursuing resources that are not free. Keep in mind you usually get what you pay for :arrow: . However I think Chris has done an outstanding job with this web site and I recommend it to all the networking “students” that I know .

Chris you may recall it was me who brought it to your attention that there is a link in the Academy Curriculum to this site. That is what brought me here for my first visit . That one link is to your discussion on Route Poisoning. ( www.firewall.cx/distance_vector.php ) I’m not sure that is an endorsement as to the absolute correctness of the entire site :wink: . But still that is quite the complement to get from a curriculum writer for Cisco. That’s my way of saying great job but please don’t let it go to your head :) .

Sorry if I offended anyone :oops: . I certainly did not think that recommending books, classes, web sites, etc. would be offensive . Research does mean the use multiple resources and the networking students I recommend this site to includes people enrolled in academy courses .

I'm not offended, I just think people should be able to feel that they can post their thoughts on topics. Giving references for people is great, I do it all the time. The thing is, a lot of times when you read something, you might miss a single point that will mess up your entire understanding of a topic. Mew, you have a lot of knowledge and know how intricate networking really is -- so I'm sure you know it's easy for people to miss some points.

I am constantly bouncing my interpretation of my studies off of my mentors who have more experience and knowledge than me. Many of the members on this forum I consider a mentor to me. I feel this is the third most important factor in my development behind my own initiative and on the job experiences.

As far as accuracy of responses, if someone posts a reply, and they are wrong, I have never seen it slip by in this forum. That is a testament to people like Mew who really know their stuff. That's why in my view, its important for people to post freely, so if they have a wrong idea they can be corrected. In the long term this will help us all because who knows, maybe someday you'll end up working with someone who reads this site. I know I want to work with competent, knowledgable people.

dear mew, how were previous routing protocols wasting ip addresses?