atcomsystems.ca/forum Forums VOIP Phones & IP PBX Networking IP Addressing and Subnets.

Not clear? Each local area network (think small ofice suite) has a network number and each computer has a computer number. Two computers that have the same network number are on the same network, and two computers that have different network numbers are on different networks.

If a computer knows:

1. it's own ip address
2. another computer's ip address, and
3. it's own subnet mask, it can figure out whether or not both computers are on the same local area network.

Yes, I understand it. What I was trying to say is that most people need to be warmed up to the whole topic before you can just throw binary at them. Your explanation requires a lot of ancillary knowledge that you are taking for granted.

kumba you have dashed my hopes to become a technical instructor!

Let me try it this way. Each house has a number and each street has a name. If you are on the same street as another house, it is probably in your local area. How is that?

I was getting around to the idea that if two computers are on the same local area network (think cable) then they can talk directly to each other. Think of it as working in the same room as someone else. You can just shout across the room.

However if two computers are on different local area networks, then they need a go-between computer to communicate. This go-between computer is connected to both local area networks and passes messages from one LAN to another. Think of it as a secretary who sits in the doorway between two rooms. If you want to talk to someone in the next room, you shout her the message, and she shouts it to the person in the next room.

Can anyone tell me what we call this go-between?

Your fired!

Way too simplistic and vague. That explanation does not even come close to explaining how a subnet mask and ip address work together which was the original question.

The 1st explination said what a Subnet did, but the binary part may be where I can see where question marks start shooting out from some people's head. Throw out a bit of AND, OR, NOT Boolean to make the rest of the follows dizzy.

I like the stream of 1's and 0's on the earlier port, While it doesn't explain what a subnet mask is, it does visualize why only some numbers can be a subnet mask (related to the question at the time). It still requires some understanding of what binary is and how it relates to the numbers people see as it relates to IP, altho that was also explained in the same post.

If someone read all these posts and still don't knbow what a subnet does, then I am not sure of a better way to explain it.

Maybe instead of a secretary (router) it was a mail runner guy for a corporate offce.

Letter for Bob. His office number is 192.168.0.100.
The mail guy is at office 192.168.5.20. He looks at the subnet sign on the wall. Hmm, it says 255.255.255.0.
All the 255s = XXX, The 0's = OOO
192.168.000.100
XXX.XXX.XXX.OOO
192.168.005.20
XXXs have to match.
The 005 does not match 000, so mail runner knows Bob is not at this building. He will give the letter guy in the mail truck. He will send it to the correct building where Bob is located.


Well, that was the best I could come up with. I know that it does not explain subnetting with numbers other then 255, which was also part of the original qustion.

What does a subnet mask do? It tells the computer how much of its ip address reprsents the network it is on and how much of its ip address represents its number on the local area network.

How does it do that? I think that was explained above. But think of it as a mask put over the ip address. If you look thru the zeros in the network mask, you see your host number. If you look thru the ones, you see your network number.

Whoever invented IP decided that ip addresses would be fixed in length but that some local area networks could be larger than others.

By the way, the subnet mask is set on the computer but NEVER transmitted to another computer. A potent source of misconfiguration!

There are only 10 kinds of people. Those who know binary and those who don't.

I like that one. :rofl:
I have seen it before, but it I still like it.