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Discussion Starter · #1 ·
Ok I recently posted in another post about my intrest in unattended WinXP installs. I'm currently going to school for my A+ cert and am on the networking section.

I am so lost on what exactly subnet masking is and what it does. I seem to learn best by simple analogies when I need to grasp a new concept so here is my question/plea.

If a default gateway is an apartment and the hosts are the apartments, what does that make the subnet mask?

If anyone can help me out with this I would greatly appreciate it as I am totally baffled when it comes to subnet masks. Thanks in advance.
 

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The best advice i can give you is to keep at it, subnetting is a tough concept to grasp at first but once you do, and you will, it will seem so easy.

All a subnet mask does is specify what network (subnet) you are on.
 

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A good IP Address analogy:
The network address is the street address for an entire apartment complex.
The host IP Addresses are the specific buildings in the apartment complex
The apartments are the ports, each housing a different application (or vacant). that is, a web site is in apartment, or port, 80; outgoing mail is in apartment 25, incoming in apartment 110.

The first address is the entire complex as a whole. The very last address is the broadcast address (coupon fliers go to all buildings, addressed to "Resident"). The individual building addresses (valid host addresses) fall in between.
 

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Discussion Starter · #5 ·
the subnet would be the separate floors of the apartment building and can only see into the apartments on their floor
I KNEW IT! I kept thinking along that analogy that if the default gateway is the building, and the hosts are the apartments than the subnet must be the floors.

Thanks a bunch for the help guys I grasp some concepts easily but networking just seems to be my bane lol
 

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Discussion Starter · #6 ·
A quick question again. My book says that the subnet mask "masks" the network address in the IP address.

My question is why? Why do you need the subnet mask to do that? Is it for security purposes or for efficiency?
 

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It is to separate different networks like a 192.168.1.1 network and 192.168.2.1 network. If there were no subnet mask then everything would be one big network and it would be a huge mess.
 

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Discussion Starter · #8 ·
ok and just to test and see if I am learning this right I am going to assume that the IP you just listed is a class C right?
 

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Discussion Starter · #10 ·
By default yes, but keep in mind that it can be any class is want it to be by changing the subnet mask.

But I thought that the class wasn't determined by the subnet but by the IP address range? or is it a mixture of the 2?
 

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Ok... A subnet mask its the one who are going to determine wish octet HAVE to be the same, theres three different class of subnets (A, B and C)

Class A (255.0.0.0)
On this subnet you're saying that only the first octet has to be the same
eg. of class A

10.0.0.1

10.25.25.45
10.58.100.200
10.20.30.40
On this example we're saying that we're on the same subnet, The default gateway is 10.0.0.1, from there you can use 254 numbers on the second octet and another 254 numbers on third and 254 on the fourth octet.

On class B (255.255.0.0)
172.16.0.1

172.16.10.20
172.16.20.10
172.16.50.60

Its the same example but on this one we're saying that the first two octets are the one who determine the IP address

Class C (255.255.255.0)
192.168.0.1

192.168.0.2
192.168.0.254

The examples that i give above are examples of privates IP addresses except on Class B, you have the opportunity to use more IP

eg. 172.16.0.1 or 172.17.0.1, its better like this 172.16 - 32.x.x

well its not that difficult to understand, with your example THE BUILDING its the subnet, and if you go to a different building you'll have different set of rooms or floors.
 

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the subnet would be the separate floors of the apartment building and can only see into the apartments on their floor
Not exactly ... all the subnet mask is there for is to help identify a HOST from a NETWORK, and to help determine if two addresses are on the same logical network.

When you convert from dotted decimal notation (255.255.255.0) to Binary (11111111.11111111.11111111.00000000) the consecutive "1's" indicate the NETWORK bits, everything after compose the HOST bits.
 

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But I thought that the class wasn't determined by the subnet but by the IP address range? or is it a mixture of the 2?
The subnet defines the class. Think of it, how do you know what address is a class C address? You look at the subnet mask, that is what tells you the class.

Example:

IP address = 192.168.1.1
Subnet Mask = 255.255.255.0

What class is this address? Class C because of the subnet mask.

Example:

IP address = 192.168.1.1
Subnet Mask = Not telling you

Now tell me what the class of this address is. You could assume it is the default class c mask above but you can't prove it can you? You don't have the subnet mask so therefore it could be any class. OK, i'm going to say the subnet mask for the above example is 255.0.0.0.

Now can you tell me what the class is? Yes you can because i gave you the subnet mask. Answer = Class A
 

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Discussion Starter · #14 ·
Ok I think that I got it but let me know if this is right:

A class is NOT determined by by the IP range but by the subnet. In addition the subnet is used to mask part of the IP address and to help determine the network and host that owns that IP address. So by that logic an IP address can be any range and be any class if one does not know the subnet.

Is that about right? And thanks for your patience with me on this lol
 
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