IP Addressing

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Contents

IP Addressing is fairly easy, and if you've ever run networks on Unix, Windows, Linux, or BSD it's practically the same here.

Subnetting[edit]

Without going too deep into the technical inner workings of IP networks, thier size and range are determined by what are called subnet masks. Subnet masks basically tell a computer what part of the ip address holds the information about what other ip addresses are directly connected to it. In other words, for a computer to have the ip address of 192.168.1.1 and a subnet mask of 255.255.255.0 tells the computer that the ip addresses 0-255 are located on the same network segment it is, and that it doesn't need to talk to any routers to communicate with them.

To understand different subnet masks and their ranges, you need to understand that a subnet mask is a decimal representation of a binary number. In the case of the normal 255.255.255.0 subnet, it is represented in binary as: 11111111.1111111.1111111.11111111.00000000. The reason why you might want to change the subnet mask would be if you had a limited amount of IP addresses, and needed to split a range into multiple ranges which would be routable. For instance, assuming you only had 256 ip addresses (192.168.1.0-255), and you had two APs which needed to use those numbers, you'd divide create two smaller subnets. To do that, you'd need to add a 1 to the last group of 0's and convert that number from binary to decimal. In binary, the 255.255.255.0 subnet after adding a 1 would look like this: 11111111.1111111.1111111.11111111.10000000. When converted to decimal, it would look like: 255.255.255.128. The affect of doing this would allow you to create two networks, 192.168.1.0-127 and 192.168.1.128-255. You can keep doing this until you get to the subnet of 255.255.255.252. That is the smallest useful subnet, with two usable IPs and two reserved IP addresses.

A small table with the various subnets likely to be used in Star-OS networks:

Binary Dotted-Decimal Slash Notation Total IPs Usable IPs
11111111.11111111.11110000.00000000 255.255.240.0 /20 4094 4092
11111111.11111111.11111000.00000000 255.255.248.0 /21 2048 2046
11111111.11111111.11111100.00000000 255.255.252.0 /22 1024 1022
11111111.11111111.11111110.00000000 255.255.252.0 /23 512 510
11111111.11111111.11111111.00000000 255.255.255.0 /24 256 254
11111111.11111111.11111111.10000000 255.255.255.128 /25 128 126
11111111.11111111.11111111.11000000 255.255.255.192 /26 64 62
11111111.11111111.11111111.11100000 255.255.255.224 /27 32 30
11111111.11111111.11111111.11110000 255.255.255.240 /28 16 14
11111111.11111111.11111111.11111000 255.255.255.248 /29 8 6
11111111.11111111.11111111.11111100 255.255.255.252 /30 4 2
11111111.11111111.11111111.11111110 255.255.255.254 /31 2 0
11111111.11111111.11111111.11111111 255.255.255.255 /32 1 0


You might find this calc handy - http://jodies.de/ipcalc