Subnets

Hi again, I'm seeking your aid with a doubt I have, let’s say I have my router connected to an ISP, and to that router I'm going to connect some switches to distribute the network on 200 different computers. Now out of this 200 computers I want to create different subnets, one with 10 computers, one with 30, one with 100 and another one with 60.
I'm thinking since the most computers I need is 100 I would use a subnet like this 255.255.255.128, but, would I have to use that subnetmask for all the subnets? I guess the question is: can the single router manage different subnets to, for instance, set a subnetmask of 255.255.255.140 for the subnet with 10 PCs and a subnet mask of 255.255.255.129 for the one with 100? This considering the setup with a single router and switches that I descibed.
For example, if I wanted 2 subnets, one with 10 PCs and one with 25, then one of them would have a 255.255.255.240 subnet mask and the other would have a 255.255.255.224, so in practice, the address range for the first one would be 192.168.1.0->192.168.1.15, and then would the next one go from 192.168.1.16 to 192.168.1.47?
And then something could happen were, for instance, I wanted a third subnet that holds 150 PCs, then the subnet (255.255.255.0) wouldn’t fit on the remaining space, in that case I just go to 192.168.2.X?

 

Thats called VLSM(variable length subnet masking), and yes it can be done. you should research VLSM and subnetting. its "must know" stuff if youre doing this kind of thing.

The masks you can use are 128|192|224|240|248|252|254|255

The last one that you can use is 252, usually used on point-to-point connections. a mask of 255.255.255.252 allows two hosts, the network address, and the broadcast address.

 

Sorry, i should probably add you could just create vlans and use the same mask. it would be less work to create some vlans on your switch and use the same mask for each vlan. so 192.168.1.0 255.255.255.0 for vlan 1, 192.168.2.0 255.255.255.0 vlan 2 and so on.

you dont really need to subnet since its all private IPs youre using anyway. no need to conserve addresses.

 

Ohh okok I get it, so I guess subneting is more of an issue with limited IPs, like in the case of public addresses, thanks alot steve you've been very helpfull, both your information about variable length subnet masking and now this have really helped me understand how that works a bit better.

 

VLANS is the way to go for sure.

 

Subnetting is mostly used when you have a block of addresses, say the 200.10.10.0 network and you have more than one network you need to assign addresses to. you can subnet this 200.10.10.0 network into smaller networks.

looking at the subnet mask 255.255.255.0, the entire 200.10.10.0-255 addresses are used for one network. if you have 25 hosts per network, and 6 networks you need to assign addresses to using only the 200.10.10.0 block of addresses, youll have problems.

so you subnet. the 255.255.255.0 mask turns into a 255.255.255.224 mask, allowing 30 hosts per network. this gives you enough addresses to assign to your hosts in each separate network you have to assign addresses to.

When you use private addresses, which 192.168.1.0 is, you can use as many of those addresses as you want. so 192.168.1.0-255, 192.168.2.0-255, and so on. if you have more addresses than class C addresses allows, you can go to a class B (172.16.0.0 255.255.0.0) or even class A (10.0.0.0 255.0.0.0).

I hope i explained that well enough without going into too much detail.

This explains classful addressing. I didnt go into classless...