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So, about those subnets.

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#1 Cyreous Media

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Posted 13 May 2014 - 12:13 PM



As I pursue an A+ Certification, there are a few topics that I've not understood from my primary source of information and I'll scour the web for more explanation to achieve an actual understanding so I'll be able to be a useful IT tech when the day comes. When it comes to subnet masks, however, everything I can find online still leaves me not understanding.


I suppose my biggest confusions are these, and they are based on the parts of subnet masks I think I do understand, so if I'm incorrect then please feel free to correct me:


The subnet mask tells the internet as a whole where to look for the individual device; so the hierarchy is the web finds my computer's subnet mask (which brings it to a subnet?), and once there it finds the specific device (My computer) based on the IP address. If I'm understanding it right then its just like coordinates; you can't find a specific geographical spot unless you first have the degrees; without the degrees the minutes and seconds would be useless because the same minutes/seconds data at different lat/long would yield a different but real result. Now assuming I'm correct on all of that, how can there only be four subnet masks?,,, and My mind can't wrap around only four masks being able to help narrow down the (i'm assuming) hundreds of thousands if not millions of computers connected online. The other thing that I don't get is why they exist in the first place, because my IP address is my MBP's specific online ID tag, in a manner of speaking, and as I understand we've run out (or are running out of) IPv4 address to hand out and thats why we've developed/are developing IPv6 which bumps from a 32 bit architecture all the way up to 128 bit architecture; we skipped the 64 bit level so that there are so many new IP address that in the foreseeable future we won't run out again.......so why subnet masks? That also brings up a few questions about IP addresses and DHCP but I'll look into it more before I bother all of you.


If anyone could clear this up I'd greatly appreciate it. I'd rather not a link to a forum because those are pre-developed explanations that don't clear up my confusion; I've probably read half a dozen of them already, although I'll still be grateful if you do at least that much.


Good Day

-Cyreous Media

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#2 CaveDweller2


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Posted 13 May 2014 - 01:45 PM

There are not 4 subnet masks. Back when this thing called the internet was just a kid they developed IP version 4(IPv4) and did what they called classful addressing. That is where the terms Class A, B, C. 


Class A addresses are - to and uses the subnet mask of 

Class B addresses are - 128..0.0.0 to uses the subnet mask of

Class B addresses are - 192..0.0.0 to uses the subnet mask of 


And this was fine for many years but then the internet grew up and when it did it blew up in size. All of a sudden this addressing scheme didn't work. It didn't help that the body that handed out addresses did a horrible job at it in the beginning. They gave huge blocks of addresses to companies because back then no one knew how huge it would get. So to help save IPv4(which they shouldn't have done but that's my opinion) they came up with subnetting. And what this does is takes a single network address and divides it up into smaller networks with X amount of hosts on them. 


Take a piece of paper and write out 128 64 32 16 8 4 2 1. All of those added up = 255. So when you see a subnet mask that is - write that out in binary. The 255's are all 1's but the 248 is:


128 64 32 16 8 4 2 1

   1   1   1   1  1 0 0 0

Which is 128+64+32+16+8 = 248 = 11111111.11111111.11111000.00000000 every where there is a 1 = the network. everywhere there is a 0 = a host. 


I have thought about this for a while and the only way to understand subnetting is to do it....A LOT. Once you get the concept it's fairly easy to understand. But I'm not going to type out something to can find on youtube, it would take hours. Just understand that they did subnetting and private addressing to help IPv4 live longer. 


With IPv6 there will be no subnetting. Everything on the planet will have a routable IP address.


 http://itknowledgeexchange.techtarget.com/whatis/ipv6-addresses-how-many-is-that-in-numbers/  <--is very cool and does a good job putting IPv6's number of addresses in a easy to see and read format. And I think you'll understand why we'll not have to worry about addresses for a very very long time








Hope this helps thumbup.gif

Associate in Applied Science - Network Systems Management - Trident Technical College

#3 Kilroy


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Posted 13 May 2014 - 01:47 PM

I'll give you the sad, sad truth about subnetting.  Unless you are in network design this isn't going to be part of your life.  Even worse, once IPv6 catches hold, it won't be something you need to know since there are enough addresses for anyone who has ever lived to have one multiple times over.


While there are five classes (A, B, C, D, and E) of subnets you can create even more subnets if needed and they all have different subnet masks.  This is information that will be covered if you pursue your Network+ certification.  Most of the networks you're going to work on will be the 10.x.x.x or 192.168.x.x networks.  If you're not designing the network this information will all be provided to you.


Being in the business I recommend learning the information that you are going to use or want to use, don't spend too much time on the things you're not going to use.


You're confused on how routing works.  The basics are either it is on your network or it isn't.  If it is not on your network it goes out your gateway and is routed on.  How Packet Travels in Network is an entertaining 13 minute video describing the process.

#4 Sneakycyber


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Posted 15 May 2014 - 05:30 PM

To add more to the mix if your goign to take the cisco CCNE or CCNA you will need to know how to subnet. Also IPV6 does not require subnetting however in our life time there will always be someone who has a private network that uses IPV4 you will still need to know how to subnet to pass the certification exams. Lastly there are easy online caculators that will do the math for your LEARN THE BINARY the calculators wont be there on the exam. You can use the calculators to check your work.

Chad Mockensturm 
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Certified CompTia Network +, A +

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