Subnet Mask

Just wanted to start up a topic about subnet mask. It can get confusing but it's really not that difficult if you practice often and take the time to understand the concept.

If anyone wishes to contribute to this thread, please do, especially Cisco professionals with extensive knowledge about subnetting. Maybe we can practice together and come up with questions and answers to different subnet masks, broadcast addresses, network addresses and IP host ranges.

CIDR (Classless Inter-Domain Routing Notation).

255.0.0.0 is 8 bits. /8

255.255.0.0 is 16 bits. /16

255.255.255.0 is 24 bits. /24

255.255.255.255 is 32 bits. /32

The 8 special numbers for the subnet mask are 128, 192, 224, 240, 248, 252, 254, 255.

Subtracting these numbers from 256 tells what the network increments are.

Network addresses are always even numbers and broadcast addresses are always odd numbers.

Anything in between the Network Address and Broadcast Address is the IP host range.

Class A (1-126) subnet mask default 255.0.0.0 /8
Class B (128-191) subnet mask default 255.255.0.0 /16
Class C (192 - 223) subnet mask default 255.255.255.0 /24

32 bits in an IP Address separated by decimals which is called dotted decimal notation.

127 can never be used in the first octet because it is the loopback address. An IP address class is identified in the first octet of an address.

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Comments

miller811

or you could start here....
http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html

Technology1

That's a great thread. I like that thread.

Thanks. Lots of useful information about subnetting there.

miller811 wrote: »

or you could start here....
http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html

sthompson86

I am scared to read another way of subnetting, for it may corrupt my current process lol

VAHokie56

sthompson86 wrote: »

I am scared to read another way of subnetting, for it may corrupt my current process lol

That link provides randomly generated questions on subnetting not technique on how to do it. This is a great site for people who wish to sit for the exam, I spent hours on that site with a timer until I could answer any of the questions in under 10 seconds.

VAHokie56

I stand corrected I blindly assumed he posted this site subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online

whomp ...whomp

Mierdin

sthompson86 wrote: »

I am scared to read another way of subnetting, for it may corrupt my current process lol

Subnetting's not one of those things that you can figure out one way to do, then be blind to all other methods. You should probably explore other sources. I know I didn't really understand subnetting until I'd hit at least 10 resources that walked me through it, and made me truly understand it.

Technology1

It takes practice, but little by little you pick up on more and more as you keep practicing with it. I wouldn't say it's exactly easy, but when you start to get better at it, it's a good feeling.

The 8 numbers to always remember are 128, 192, 224, 240, 248, 252, 254, 255.

Mierdin wrote: »

Subnetting's not one of those things that you can figure out one way to do, then be blind to all other methods. You should probably explore other sources. I know I didn't really understand subnetting until I'd hit at least 10 resources that walked me through it, and made me truly understand it.

mikej412

Subnetting is what separates the people who have a future in networking from the users.

Technology1

Just looking at all those certifications you have is very impressive.

I'm still not perfect with subnetting but I do practice often and have a good basic understanding of it. There is always more to learn and it's fun and hard at the same time. When I think of subnetting I think of a smaller network (sub-network) within a larger one. Different network increments, network addresses (even numbers), ip host ranges, valid hosts, broadcast addresses (odd numbers). There's a lot to learn.

128, 192, 224, 240, 248, 252, 254, 255

hub - layer 1 (physical)

switch - layer 2 (data link)

router - layer 3 (network)

email - layer 7 (application)

mikej412 wrote: »

Subnetting is what separates the people who have a future in networking from the users.