# what does the 24 mean in 10.0.0.0/24?

#### nerdcore

##### Limp Gawd
Like the title says...what does the 24 mean in 10.0.0.0/24. Saw this in a proposed network layout and was wondering. Thanks!

#### Darthkim

##### Limp Gawd
24 = 255.255.255.0
16 = 255.255.0.0

beat me to it =P

#### Morpheus256

##### 2[H]4U
yall beat me to it, and i was screwing around with that stuff today in class (grumbles about how big of a pain in the ass subnets are)

#### Zlash

##### 2[H]4U
Subnets are pretty easy once you learn to do it in your head.

#### Wiseguy2001

##### 2[H]4U
Originally posted by Zlash
Subnets are pretty easy once you learn to do it in your head.
Thats the hard part

Zlash - how long did it take to get all those certs?

#### Icewindius

##### Gawd
I reread the subnet chapter last night and it just isn't sinking in. And the OSI layer is killing me, I swear I have some kinda mental block for anything networking wise.

I don't think im cut out for networking, probably move to MCSA after Network + is done....

#### figgie

##### Supreme [H]ardness
Originally posted by Icewindius
I reread the subnet chapter last night and it just isn't sinking in. And the OSI layer is killing me, I swear I have some kinda mental block for anything networking wise.

I don't think im cut out for networking, probably move to MCSA after Network + is done....

over complicate things

subnetting is all math

#### bdavids1

##### Limp Gawd
Originally posted by nerdcore
Like the title says...what does the 24 mean in 10.0.0.0/24. Saw this in a proposed network layout and was wondering. Thanks!
It means 24 1's in a row:
Code:
``````11111111111111111111111100000000

1111 1111  1111 1111  1111 1111  0000 0000

1111 (binary) = F (Hex), so we get:

F F  F F  F F  0 0

FF.FF.FF.00  -> 255.255.255.0``````
A /23 would correspond to 23 1's, or 255.255.254.0.

#### bdavids1

##### Limp Gawd
Subnet masks are easy: convert the netmask and the IP address into binary. It only makes sense in binary -- you're using a bitmask.

Example:
You are on the network 10.3.4.0/22. You want to talk to the computer 10.3.6.14. Is that computer on the same network as your computer? That's THE question subnet masks address. Here's how to answer it.

1) Convert your network number to binary
2) Convert target IP to binary
3) Apply subnet mask to target IP

Code:
``````/22 is the following subnet number (netmask):

1) 10.3.4.0 in binary:
00001010 00000011 00000100 00000000  (Network #)

2) 10.3.6.14 in binary:
00001010 00000011 00000110 00001110  (target IP)

00001010 00000011 00000110 00001110  (target IP)
--------------------------------------------------------------------------
00001010 00000011 00000100 00000000  (Target Net #)

4) Compare Target Net # with your Network #:

00001010 00000011 00000100 00000000  (Target Net #)
00001010 00000011 00000100 00000000  (Network #)

They are the same, so the target computer is on the same network as your computer.``````

In step 3 you perform a bitwise AND. If there's a 1 in the netmask, copy the bit from the target IP down to the Target Net #. If there's a 0 in the netmask, write a 0 in the Target Net #.

All that's needed is the ability to convert from decimal to binary. Normally Hexadecimal is used as an intermediate step, since it's trivial to convert from hex to binary. Windows calculator can do these conversions for you, or if you do it enough you'll learn to do it in your head.

#### Lime

##### Gawd
Hex is annoying, but easy. the OSI model is rather easy as well, I mean just make a little thing that helps you remember the 7 layers.

Application
Presentation
Session
Transport
Network
Physical

Please Do Not Throw Sausage Pizza Away

=)

#### Zlash

##### 2[H]4U
Zlash - how long did it take to get all those certs?

Subnet masks are easy: convert the netmask and the IP address into binary. It only makes sense in binary -- you're using a bitmask.

Man that's the long and hard way. 256 - mask is all ya need to know.

#### enforcer17

##### [H]ard|Gawd
Originally posted by Lime
Hex is annoying, but easy. the OSI model is rather easy as well, I mean just make a little thing that helps you remember the 7 layers.

Application
Presentation
Session
Transport
Network
Physical

Please Do Not Throw Sausage Pizza Away

=)

I use:
All People Seem To Need Data Processing. And its in order.

All
People
Should
Try
Nude
Dancing
Probably

Works for me!!

#### Icewindius

##### Gawd
Oooooooohh OK, now it makes more sense.

I need to stop thinking of the 4 octets and go back to binary and it makes much more sense. Still gotta figure out how many hosts I get per subnet and how many I loose...

I'll never pass CCNA

#### BobSutan

##### [H]F Junkie
Originally posted by Lime
Hex is annoying, but easy. the OSI model is rather easy as well, I mean just make a little thing that helps you remember the 7 layers.

Application
Presentation
Session
Transport
Network
Physical

Please Do Not Throw Sausage Pizza Away

=)

I was taught it as

All People Seem To Need Data Processing

#### Lime

##### Gawd
those are both valid ways I suppose, but it goes 1-7 from the BOTTOM up =) starts at Physical

#### enforcer17

##### [H]ard|Gawd
Originally posted by BobSutan
I was taught it as

All People Seem To Need Data Processing

HAHA cool, exactly what i said on the first page:

I use: All People Seem To Need Data Processing. And its in order.

Good teaching i guess!!

#### Wiseguy2001

##### 2[H]4U
Originally posted by BobSutan
I was taught it as

All People Seem To Need Data Processing

Thats how I learnt, but I made a change to it 'all people seem to need Data protection' handy not only to networking people but also every one else.

Nerdcore  are you currently studying Net+/ccna? If so dont worry too much if you have read a chapter and dont understand much of it (at first), networking is a very vast field. And it takes time to understand all the concepts. As you study more stuff, what you didnt quite understand previously will come clear to you.

#### BobSutan

##### [H]F Junkie
Originally posted by enforcer17
HAHA cool, exactly what i said on the first page:

Good teaching i guess!!

Darn. Thought I was the first to bring that one to light. Suppose that's what I deserve for skimming threads too quickly.

#### Icewindius

##### Gawd
Nerdcore  are you currently studying Net+/ccna? If so dont worry too much if you have read a chapter and dont understand much of it (at first), networking is a very vast field. And it takes time to understand all the concepts. As you study more stuff, what you didnt quite understand previously will come clear to you

That probably applies to me too. There just so much to this field I just cant retain it all. Shit, i've already forgotten the COM IRQ settings and stuff.

Basically im like this, If I dont use it on a day to day basis, I WILL forget it. Other peeps pretty much I assume just remember everything.

#### PopeKevinI

##### 2[H]4U
Originally posted by Icewindius
That probably applies to me too. There just so much to this field I just cant retain it all. Shit, i've already forgotten the COM IRQ settings and stuff.

Basically im like this, If I dont use it on a day to day basis, I WILL forget it. Other peeps pretty much I assume just remember everything.

You're in luck...COM ports are mostly vestigal now, and you rarely need to know the IRQs

As for retention...I recommend that you read any book you study three times, especially if you're trying to grasp something like networking without much experience. Take notes every time, writing down anything you consider important or difficult to remember. Compile all your notes, and study them before a cert test. By then, you'll have seen it so often that you'll recall it when you see a question over it, whether you think you know it or not.

For the record: I have no clue what th COM IRQs are. In seven years of tech work, I've never needed that information, except on my A+ exam.

##### [H]ard|Gawd
studying for the ccna was fun for me. learning all that crap made me feel all warm and fuzzy inside. a friend of mine is gonna sell me 2 2501's for like 130 for my ccnp lab, cant wait all i need now is a 1924 switch with FE so i can do vlan routing

#### Morpheus256

##### 2[H]4U
All People Seem To Need Dominos Pizza

#### Wiseguy2001

##### 2[H]4U
My study technique, is to read the books once and do as much hands on stuff as possible. Then grab the exam syllabus and write down everything the u know under each point (use colour coding for this), then go though the book and fill in all the gaps. If you find you know very little about a section then reread the chapter.

Using this data to test yourself and fill in the blanks has to be the best way of making sure that you everything (in detail) that you need to pass exam.

#### bdavids1

##### Limp Gawd
Originally posted by Icewindius
Oooooooohh OK, now it makes more sense.

I need to stop thinking of the 4 octets and go back to binary and it makes much more sense. Still gotta figure out how many hosts I get per subnet and how many I loose...

I'll never pass CCNA
Yeah, binary is the key.

How many hosts is easy too. Count how many 0's you have in the netmask (32 minus the /number). Then it's 2^#of 0 hosts on that subnet. For a /24 you have 8 (32 - 24) 0's. 2^8 is 256, which is what you would expect.

A /23 would have 32 - 23 = 9 0's. 2^9 = 512 hosts

A /25 would have 32 - 25 = 7 0's. 2^7 = 128 hosts.

#### Zlash

##### 2[H]4U
A /23 would have 32 - 23 = 9 0's. 2^9 = 512 hosts

A /25 would have 32 - 25 = 7 0's. 2^7 = 128 hosts.

Nope, 510 and 126. Don't forget to subtract 2. 2^n-2

#### bdavids1

##### Limp Gawd
Originally posted by Zlash
Nope, 510 and 126. Don't forget to subtract 2. 2^n-2
OK, I'll almost buy that. It should be 511 and 127 -- you subtract 1, for the broadcast address (the all 1's node). The router is a host on the network. If you have one router, then you can fit 510 or 126 other hosts on the given subnet.

#### Wiseguy2001

##### 2[H]4U
Zlash is right

.0 - is the wire or network address

None of which can be used to connect a device

#### Zlash

##### 2[H]4U
Not necesarrily .255 or .0 , but 2 of the hosts are unusable on any given subnet.

Where'd you learn to subnet bdavids?