255+ IP Addresses

Well, a standard class C subnet like 192.168.1.0 with a subnet mask of 255.255.255.0 provides 254 usuable IP addresses. The only addresses that cannot be used are 192.168.1.0 (this is the network) and 192.168.1.255 (this is the broadcast).

What you could do, is to supernet two class C's together. So, you could still use 192.168.1.0 as the network with a 255.255.254.0 subnet mask and then you would have 510 usable addresses. Your network is still 192.168.1.0 and the broadcast would be 192.168.2.255 and the usable addresses would be 192.168.1.1 through 192.168.2.254.

In your example, you seem to suggest using a 172.168 network....but this is a legitimate IP address. You should use a special non-routable address of either 10.0.0.0/255.0.0.0 or 172.16.0.0/255.255.0.0 or 192.168.0.0/255.255.255.0.

But with your example, if you tried to use 172.168.0.0 as your network with a 255.255.0.0 subnet mask...you could actually have 65,534 addresses on this network. you could use 172.168.0.1-172.168.0.255 (first 250+ addresses)and 172.168.1.0-172.168.1.255 (next block of 250+ addresses), and 172.168.2.0-172.168.2.255 (next 250+ addresses), and 172.168.3.0-172.168.3.255 (another 250+)...and so on. The only non usable addresses are the network (172.168.0.0) and the broadcast 172.168.255.255

byocky said:

If I subnet 2 class C's together as you suggest, will all devices communicate with all others through a set of switchers, at present there are no routhers on the network, just switches.

In this case, you aren't subnetting the 2 class C's together, but rather supernetting them together.

Subnetting takes a single network, like a class C and makes more networks out of them. It breaks them down into smaller blocks of hosts. For example, 192.168.1.0 network with a 255.255.255.0 subnet mask, gives you 254 hosts between 192.168.1.1 and 192.168.1.254. Any host in that range is on the same network and does NOT need a router to communicate. If you subnetted that network, you would use a subnet mask such as 255.255.255.224. This would give you 8 different networks, each with 30 usable host addresses.

So, network 1 would be 192.168.1.0 with usable addresses from 192.168.1.1 to 192.168.1.30, with a broadcast address of 192.168.1.31. The next network would be 192.168.1.32 and your valid hosts would be 192.168.1.33 through 192.168.1.62, with 192.168.1.63 being the broadcast and the next network starting at 192.168.1.64. Machines on the same network can talk to each other. Machines on different networks would need to be routed to each other.

With supernetting 2 class C's together, instead of further dividing 255.255.255.0 down, you go the opposite way and aggregate them together. Thus, 255.255.254.0 or 255.255.252.0, or 255.255.248.0. Since you are making the 1 single network bigger, you don't need a router for the hosts to talk to each other, they would be on the same logical network.

byocky said:

If I were to use a SN of 255.255.243.0 would this give my the addresses between 192.168.1.0-192.168.3.255?

You cannot use .243 as a subnet mask. You have to use binary numbering. With a ipv4 address, you have 4 octets of numbers and each are 8 bits in size. So, you have 00000000 if all bits are off and 1111111 if all bits are on. Going from RIGHT to LEFT, with binary, you get 128,64,32,16,8,4,2,1.

A subnet mask of 255.255.255.240 would be written as 1111111.1111111.1111111.11110000. In the last set of numbers, you have 1's in the (128+64+32+16) positions and if you add them up, it comes to 240. The 1's represent the networks, and the 0's represent the hosts. Since each position can be either a 0 or a 1...you have 2 choices. So, with 4 zeros for hosts....you have 2 raised to the power of 4...or 16 hosts....but then you have to subtract 2.....(all zeroes which represent the network) (and all 1's which represent the gateway). So, you would have 14 hosts on each network in this case.

So, a subnet mask digit must be either 0, 128, 192, 224, 240, 248, 252, 254 or 255.

byocky said:

Why is joining 2 subnets in a class C better than using a class B network?

Ben

In your case, it's probably no advantage whatsoever. In a larger environment, it's highly advantageous to break up networks for security purposes, bandwidth purposes and to separate broadcast domains. But on these networks, you have to route the traffic between the networks...and you typically break up those networks with VLAN's.

Just be sure that you use the private address ranges that are reserved
10.0.0.0
172.16.0.0 to 172.32.0.0
192.168.0.0

This page does a pretty good job on explaining private ranges
IP-Adress.com - What is a private ip-address? What are private ip addresses?