Jackeen,
It's quite normal to get confused with subnetting. It took me a while when I first started, in order to understand and implementing subnetting correctly, so don't worry!
netNetbie's post is correct and defined well.
Your also thinking along the correct lines as far as your last post.
As you correctly stated, if you had one network with 250 pc, it would be necessary to 'break it up' - that is, to subnet it, in order to create smaller networks.
Breaking it up would mean that your default subnetmask for that Class C network (192.168.0.0) would change from 255.255.255.0 to something like 255.255.255.X where X's value would depend on how many networks you need to create from the original network.
In the case of extending the network with a further 250 pc's then you would definately seperate them aswell by subnetting that new network. The new range you gave - 192.168.1.1- 192.168.1.251 is valid to cover all those pc's.
The important detail you need to understand is that in practice, you never have a network (or subnet) with more than 50 pc's. Reason for this is because the broadcasts and other unnecessary traffic will flood the network and decrease the overall network performance and bandwidth availability.
This is why we always subnet networks, making life easier for ourselves.
I hope things are now clear to you!
I would highly recommend you consider reading the subnetting section once more - to help cover any weak spots you might have on the topic.
We are planning to introduce real life scenarios for the subnetting section as its one of the most popular topics on the site. It's just going to take a while to implement as we are stuck on rewritting the TCP section.
Meanwhile our kind members are helping everyone out by answering to questions and problems - and sometimes this can be more effective than simply reading a related topic.
There is so much to do - and yet so little time !
Cheers,
