88 replies to this topic

[idafioretti]

There is a game on cisco site that will help you learn binary numbers..its called cisco binary numbers game

http://cisco.com/web/learning/le31/le46/pr...ts-routers.html

[idafioretti]

actually this helps alot

[Adamf]

Lots of good tips on here. Need to try and get my head round subnetting!

[tscarry]

I have used several types of ways to do subnetting.  Unfortunately, it is something you need to know.  After the tests, use a subnet calc.  I found the site support.wrq.com/tutorials/tcpip/tcpipfundamentals.html to be pretty good.

[abbiejoy21]

I don't know if anyone has mentioned this site yet, but I found it very helpful.

www.learntosubnet.com

Subnetting is a tricky concept...but once you've got it, you probably won't lose it.

Basically you steal host identifier bits to create subnet identifiers. Remember that you can't steal network identifier bits.

[tsmith]

I don't know if this has been shared but it's a real simple way of learning subnetting.

http://www.punkwalrus.com/howto/subnetting.html

The only thing that is not explained is if you have 192.168.1.0 /24 what that means.

What that means is that in the subnet mask you have 24 bits set to 1 instead of 0.

so /24 = 11111111.11111111.11111111.00000000
    /24 = (128+64+32+16+4+2+1).(128+64+32+16+4+2+1).(128+64+32+16+4+2+1).(0+0+0+0+0+0+0+0)

/24 = 255.255.255.0 or how I think about is in 8's. Since there are 8 bits in an octect I look at it as how many times does 8 go into 24, 3 times so I know my first three octects are on and a full octect equals 255.

[npluss]

Nice info folks...iam realy halted on subnetting...hope it will not come in exam.

[dogma1029]

You can bet that if it's mentioned in the objectives then you have a reasonable chance of seeing it on the test. You will see 85 questions out of the pool of 1000's of questions that CompTIA has to pull from. I certainly wouldn't want to gamble my $200+ in the hope of not seeing a subnet question. Or more importantly have a question come up in a future job situation and look like a deer in the headlights.  

Just my opinion but I think knowing the material as best you can is the only way to go. Better to ask tons of questions here and get it down than look foolish later.  

[dazang]

I agree that subnetting is not the easiest topic in Networking.  I will probably buy a book solely on subnetting just to figure it out.  I can never get a good mathematical description of the calculations.  Obviously the authors of the books I have read are not math professors.

my 2 cents

[yoda9999]

Here are some sites to learn and practice subnetting:

http://easysubnet.com/
http://subnettingquestions.com

[sherellvette20]

I have pinned this thread. Feel free to share subnetting tips, tricks and web resources here.

I agree WIKI barely explains anything about subnetting

[sherellvette20]

Nice info folks...iam realy halted on subnetting...hope it will not come in exam.

Yep, u are right about that!

[enerside]

I would suggest for all having trouble with subnetting to focus on class C first and not move on to class Bs or As until you can do a class C quick and in your head.

128 Mask - 2 Networks - 126 Hosts - Block size 128
192 Mask - 4 Networks - 62 Hosts - Block size 64
224 Mask - 8 Networks -30 Hosts - Block size 32
240 Mask - 16 Networks - 14 Hosts - Block size 16
248 Mask - 32 Networks - 6 Hosts - Block size 8
252 Mask - 64 Networks - 2 Hosts - Block size 4

Notice a pattern here... the basics are the same.

Also, if you plan on moving up to CCNA, learn to count by 16, trust me it will help.

[rotwin]

Just wondering if this type of conversion will be on the net+ exam?


"

Converting binary to Hex is SOOO easy with this little trick.

Take, for example, the binary string 1001 1110. To convert this to binary, simple take groups of 4 binary "digits" and convert them to their decimal value. So 1001 = 9 and 1110 = 13. Now, convert this to Hex. Remember, hex values are as follows:

0
1
2
3
4
5
6
7
8
9
10 = A
11 = B
12 = C
13 = D
14 = E
15 = F

So 9 remains the same, 13 turns into D, the answer being 9D. If you have a binary value that can't be broken into groups of four equally, simply add enough zero's to the left so that you do. For example, the binary number 1010010 would be 0101 0010 -- the leftmost bit was added to make it an equal pairing.

Does this make sense?

"

[COlsen573]

subnetting is not by any means a large portion of the test. so if youre only interested about passing the test do not be TOO concerned

[valleyman1]

The books do not do justice to subnetting.  Try http://www.learntosubnet.com/ for a good understanding of it.

[thesoto]

If somebody have a dud with subnetting just look the CCNA book of Todd Lammle and forget this point for the rest of her life.... trusts me is not abs is real truth with only 30min that you can read this chapter and that's it....

[fattyfatfat]

does anyone now if subnetting is strong in the exam?

[peterjames24]

Subnetting a Class C Address: The Fast Way!


When you’ve chosen a possible subnet mask for your network and need to determine the number
of subnets, valid hosts, and broadcast addresses of a subnet that the mask provides, all you
need to do is answer five simple questions:
 How many subnets does the chosen subnet mask produce?
 How many valid hosts per subnet are available?
 What are the valid subnets?
 What’s the broadcast address of each subnet?
 What are the valid hosts in each subnet?



At this point, it’s important that you both understand and have memorized your powers of 2.
Please refer to the sidebar “Understanding the Powers of 2” earlier in this chapter if you need some
help. Here’s how you get the answers to those five big questions:
 How many subnets? 2x = number of subnets. x is the number of masked bits, or the 1s.
For example, in 11000000, the number of 1s gives us 22 subnets. In this example, there
are 4 subnets.

 How many hosts per subnet? 2y – 2 = number of hosts per subnet. y is the number of
unmasked bits, or the 0s. For example, in 11000000, the number of 0s gives us 26 – 2
hosts. In this example, there are 62 hosts per subnet. You need to subtract 2 for the subnet
address and the broadcast address, which are not valid hosts.
 What are the valid subnets? 256 – subnet mask = block size, or increment number. An
example would be 256 – 192 = 64. The block size of a 192 mask is always 64. Start counting
at zero in blocks of 64 until you reach the subnet mask value and these are your subnets.
0, 64, 128, 192. Easy, huh?

 What’s the broadcast address for each subnet? Now here’s the really easy part. Since we
counted our subnets in the last section as 0, 64, 128, and 192, the broadcast address is
always the number right before the next subnet. For example, the 0 subnet has a broadcast
address of 63 because the next subnet is 64. The 64 subnet has a broadcast address of 127
because the next subnet is 128. And so on. And remember, the broadcast address of the
last subnet is always 255.

 What are the valid hosts? Valid hosts are the numbers between the subnets, omitting the
all 0s and all 1s. For example, if 64 is the subnet number and 127 is the broadcast address,
then 65–126 is the valid host range—it’s always the numbers between the subnet address
and the broadcast address.


Subnetting Practice Examples: Class C Addresses
Here’s your opportunity to practice subnetting Class C addresses using the method I just
described. Exciting, isn’t it! We’re going to start with the first Class C subnet mask and work
through every subnet that we can using a Class C address. When we’re done, I’ll show you how
easy this is with Class A and B networks too!
Practice Example #1C: 255.255.255.128 (/25)
Since 128 is 10000000 in binary, there is only 1 bit for subnetting and 7 bits for hosts. We’re
going to subnet the Class C network address 192.168.10.0.
192.168.10.0 = Network address
255.255.255.128 = Subnet mask
Now, let’s answer the big five:
 How many subnets? Since 128 is 1 bit on (10000000), the answer would be 21 = 2.
 How many hosts per subnet? We have 7 host bits off (10000000), so the equation would
be 27 – 2 = 126 hosts.


 What are the valid subnets? 256 – 128 = 128. Remember, we’ll start at zero and count in
our block size, so our subnets are 0, 128.
 What’s the broadcast address for each subnet? The number right before the value of the
next subnet is all host bits turned on and equals the broadcast address. For the zero subnet,
the next subnet is 128, so the broadcast of the 0 subnet is 127.
 What are the valid hosts? These are the numbers between the subnet and broadcast
address. The easiest way to find the hosts is to write out the subnet address and the broadcast
address. This way, the valid hosts are obvious. The following table shows the 0 and
128 subnets, the valid host ranges of each, and the broadcast address of both subnets:


Subnet 0 128
First host 1 129
Last host 126 254
Broadcast 127 255

[mytorchedsoul]

Resolving IP address broadcast numbers and subnet ID's is one thing, but actually taking an address and figuring out how many usable addresses you'll have and all that is a completely different thing. . .  I hate subnetting.