View Full Version : networking ip addys

20-11-2002, 12:08 PM
whats the ip addys that are assigned to lans??

i've always used 192.168.0.X and 10.10.10.X but i know there's others. i have seen 10.0.0.X used but i wasn't sure if that was a valid one for lans.

also whats the difference between class A, B and C ?

20-11-2002, 12:14 PM
172.20.x.x as well I'm pretty sure. I'll have to dig it all out from my cisco notes at some stage.

The difference between classes A, B and C is the amount of nodes you can have on the network.

A Class 'C' network can have 255 -2
A Class 'B' network can have (255*255)-2
A Class 'A' network can have (255*255*255)-2

So 253, ~65000, ~16million

The reason for the -2 is because of the network(.0) and broadcast(.255) addresses.

20-11-2002, 12:17 PM
And then you get into those wonderful subnetting :D

20-11-2002, 12:58 PM
10.0.0.? seems to be the default range that DHCP gives out in windows 2000 server.

Graham L
20-11-2002, 01:00 PM
The whole 10.x.y.z is available. So you can have a large LAN. :D

20-11-2002, 02:06 PM
apart from the difference in IP addy is there any reason you should use class A instead of class C ??

thx JM i forgot about the .0 & .255.

fortunatly i've never done any really big lans that required 10.x.y.z ;-)

Graham L
20-11-2002, 02:24 PM
Who needs a reason?

There are a number of companies which use Class A for their internal networks. They buy 50000 desktops in one order. I suppose they can negotiate good prices, with the manufacturers.

I use it because it gives me lots of flexibility. (And it's one less digit to type in the first part when I am entering IP addresses. :D)

20-11-2002, 09:13 PM
The A, B, C is immaterial provided you are not connected to the outside. Certian things like ADSL modems assume a standard 192.168.1.x. The subnet mask must be 255.255.255.x, where the X is usually 0. The subnet MASK isjust that. It masks the first three octets or 24 bits of the IP address, i.e. 192.168.1. In other words you can only use the last octet (8 bits) for addressing purposes. Thus you only have 254 choices, excluding the 1 in the range. This is a Class C range and usually adequate for the home (unless you are BG, I suppose). Class A is the range to, B = to, C as above. These were originally set aside for ISP's. There is also Class D, for multicasting and Class E reserved for research. However, to repeat, it doesn't matter a toss what IP address a LAN is on as long as it doesn't connect to the outside world with an A, B, D, E address. Most ISP's will filter out such addressing, you're left in never-never land. Remember that the subnet is all important in everyone seeing each other on the LAN.