4 Replies Latest reply: Jul 29, 2010 11:55 AM by Scott Morris - CCDE/4xCCIE/2xJNCIE RSS

    the Enhanced bob man for subnetting


      i saw the enhanced bob maneuver for subnetting in the CCNA portable command guide can anyone tell me how good this is? Is it a good way to master subnetting?

        • 1. Re: the Enhanced bob man for subnetting
          Keith Barker - CCIE RS/Security, CISSP

          I wouldn't recommend it as my first choice.


          And the table in the book has an error.


          bob maneuver.png


          If not using subnet zero (old way) the 4 on the bottom row should be a 2.


          If using the subnet zero, the 4 would be correct, but the rest would not.


          Keith Barker

          • 2. Re: the Enhanced bob man for subnetting

            thanks Keith, can you suggest another simple way to be able to subnet as fast as possible. I mean a table of the sort that can aid quick subnetting?

            • 3. Re: the Enhanced bob man for subnetting
              Scott Morris - CCDE/4xCCIE/2xJNCIE

              Can we make the "Premium Bubba" version, because that just sounds much cooler than "Enhanced Bob". 


              Anyway, I've stared at that chart for several minutes now and honestly don't have a clue what I'm looking at, but I'm ok with that.


              One of the best things I can recommend is to REALLY spend time with binary.  Yes, it may take a little bit longer in the initial learning phase, but as you add to your learning, you'll find that so many things come much easier because you actually understand binary....


              Write everything out (entire IP addresses) in binary.  Yup, that will give you 32 obnoxious numbers to write.  And start drawing lines.


              When you are subnetting, you have two lines (three sections) to be concerned with.


              The first line (left-most) separates your NETWORK bits from the rest of the 32 bits.  Your second line (right-most) separates off your host-bits.  Anything left in the middle is your SUBNET bits.  And you can play around with those lines and start looking at things like how many bits are in the middle (subnet).  2^x tells you how many possible subnets you have then (and you can even decide to argue yes or no with subnet zero).


              But the catch is that the binary numbers will not scare you any longer.  Can you pick up anyone in a bar with this knowledge?  Not very likely.  Unless you happen to be at Cisco Live at the time.    but it will help a lot.  Visualize it.  Play, play, play.


              And call it the "Premium Bubba" method.




              PS.  I think I figured out the chart and its patterns, but IMHO it's too much DIFFERENT information all at once to present value.  Memorize the bit positions.  Starting from the right and going left....  1, 2, 4, 8, 16, 32, 64, 128.  That's your 8 bits.  Use the dry erase boards if you need to.  If your subnet bits are 11000000, then you have 128 + 64 to figure out how to add.  Don't forget to carry the one. 

              • 4. Re: the Enhanced bob man for subnetting

                I use a variation of "The enhanced bob", and I passed my ICND1 today, so it must be working.

                Actually, I spent part of the 15 minute tutorial-time jotting down my two tables for easy lookup during the exam. As it turned out I didn't really need it, I've memorized it pretty well these past four months, but it was nice to check my answers.


                Table should be attached as pdf if I did it right...


                I'm really bad with math, and subnetting with binaries just takes me forever, so I just do it this way, in my head, instead. The tables are more like a cheat-sheet for blocksizes, masks, bits (CIDR) and subnets.


                The table should be self-explanatory, with the CIDR-part telling you which octet you're working in (bottom is the first octet, top is the last octet).

                To find number of hosts, multiply blocksize of subnet octet with 256, and remove two (network and broadcast).


                The list of numbers (0 through 100) is just helping me move up blocks (told ya I'm bad with math - I can't even add 32 to 32 and come up with the right answer). It's just cut for lenght and reused. Dots and hyphens shows me the next hop. For every hundred I go one up from the previous, so if I'm counting upwards in increments of 16, the next number after 96 would be (when you start from the top again) 112 (the one right above the = (16-marker)).


                Not sure anyone can understand this, when I read it it sounds completely insane (much like binaries are to me). But I guess it's one of those things where you either get it or you don't.


                Hope it helps.