Getting older, not necessarily wiser!
Internet protocol Version 4 (IPV4) has been around since 1983, back in the ARPANET days. Versions 1 to 3 where mainly used in laboratory testing and never saw wide scale deployment. IPV4 is one of two addressing protocols used on the internet today, the other being IPV6 (subject for another post).
IPV4 addresses are managed by the Internet Assigned Numbers Authority (IANA). The rapid growth of the internet has depleted the availability of public IPV4 addresses. Network Address Translation (NAT) was one answer to this problem, as it allowed setting up of private non routed networks. The other answer to this issue is the development of IPV6, which has a much larger address pool.
In this post we will look at IPV4 from 10,000 feet, and discuss what you will need to know for most home networking situations.
A lot of articles on IPV4 addresses will describe them as 32 bit, 4 octets, 4 dot separated hexadecimal, or 4 dot separated decimal. The most common representation is the 4 dot separated decimal notation, for example “192.168.2.4”.
In a previous post we talked about bits and bytes, and how information is stored on a computer. The IPV4 address is 32 bits. Since a byte is 8 bits (most common definition), we can also say that an IPV4 address is 4 bytes long. Therefore four octets, decimal numbers, or hexadecimal numbers are all different ways of displaying the same four bytes. As explained in the earlier post, a single byte can have a range of 0 to 255 decimal, and 00 to FF hexadecimal. We will focus on the decimal representation, as that is the most common.
Most IPV4 addresses are public addresses and are coordinated by the Internet Assigned Numbers Authority (IANA). This is to ensure that no duplicate IPV4 addresses show up on the public network. Duplicate IP addresses are bad, and will cause a network to not function correctly.
However there are a handful of addresses that are reserved for special purposes. One such purpose is private addresses for local area networks. You will sometimes hear reference to private networks not being routable. This is a misnomer. They are routable, like any other IPV4 address. They are just not routed publicly.
Your home network is an example of a private network. When you set up your router, it will have a private IPV4 address. For example, 192.168.1.1 is used by D-Link, Linksys, and Netgear (to name just a few).
Because you can not have duplicate IP Addresses, consumer routers use NAT to hide the local private address.
For Example, you send data from your laptop which has IP address 192.168.1.100. It goes to your router at 192.168.1.1. Your router will translate the IP address of your information to match your public IP address assigned by your Internet Service Provider (ISP). Your router will also keep a record of this activity. When data comes back in through your public IP address, your router checks its records to see if it is a response to data sent from one of the local devices. It finds your record, and translates the IP address back to your laptop address and forwards you the data. If no record was found the router does nothing with the data and lets it drop.
You may have been asked to enter a subnet mask when setting up your local network. This is known as subnetting. What happens is your IP address is divided into two parts; Routing Prefix and Host identifier. Any device within the Host Identifier range can be reached directly. Anything outside of that range must go through your router to be reached.
For example, your router IP address is 192.268.2.1, and your subnet mask is 255.255.255.0. Any device with a IP address in the range of 192.168.2.1 to 192.168.2.255 can be reached directly. Any device outside that range must be routed, say 192.168.10.4 for example.
Boring Technical Stuff: Your address is 32 bits long or four 8 bit octets. The maximum decimal value for 8 bits is 255. When you enter 255 in a subnet, it blocks every single bit in that octet, thus blocking the whole octet. When you enter 255.255.255.0, you are blocking the first three octets, leaving only the last octet for your direct addressing range. Since we are blocking the first three octets (three 8 bit octets is 24 bits) the network address and subnet mask may also appear as a single entry; 192.168.2.1/24 for example.
You may be wondering about the reason for using the specific IP addresses in the examples above. These all fall into one of the public non routed private IP address ranges. You may choose any of the address ranges within a private range to use on your local network. There are three private IP address ranges, also known as Class A, B, and C depending on the number of addresses in a range.
This has been a quick overview of IPV4 addresses as they relate to your local network. I have tried to avoid some of the more technical details, while making the explanation understandable.