IP Networking Primer
For two people to communicate with one another, they need to speak a common language. For example, here I type in English and you read in English. Likewise, for two devices to communicate with one another, they need to do the same. The “languages” for devices are known as “protocols”. One of the most common protocols these days is the Internet Protocol (a.k.a. IP).
Although it has the word “Internet” in it, IP is not limited or restricted for Internet use. IP is commonly used to connect devices not hooked up to the Internet.
For two people to communicate with one another in a room full of other people not only do they need to speak a common language, they also need to address each others by name. Instead of saying, “How are you?” They need to say, “Bill, how are you?” IP is a broadcasting protocol. When an IP device sends a message, all devices on the network receive it. To send a message specifically to a device, a identifier is needed (in lieu of a name). In other words, each device in an IP network needs its own identifier, known as an IP Address. An IP Address consists of a group of 4 numbers, each ranged from 0-255. For example, 184.108.40.206 or 220.127.116.11.
Subnet and Subnet Mask
There are many reasons to group IP addresses together. The two most prominent ones are:
1) 4 groups of 0-255 numbers will only yield 4.3 billion unique addresses. There are obviously more IP devices than that in the world.
2) Some devices and the messages between them should not be exposed to the rest of the world. (Think computers in the Department of Defense, for example)
IP devices groups are called subnets. To group IP devices into subnets, another identifier is used, called subnet mask. A subnet mask is also composed of 4 groups of numbers separated by periods. In actuality, subnet mask is not as much an identifier as a “how to read me” filter. In general, 2 values are used is each number: 0 and 255. The easiest way to explain this is to use a few examples:
Device 1: IP=18.104.22.168, Subnet Mask=255.255.255.0
In this example, this device will consider any IP devices within its reach that has the same first 3 numbers (“masked” by the 255.255.255) to be within the subnet that it belongs to. If another device, say,
Device 2: IP=22.214.171.124, Subnet Mask=255.255.255.0
Sends a message, device 1 will listen in on it. However, if another device, say,
Device 3: IP=126.96.36.199, Subnet Mask=255.255.255.0
Sends a message, it will be ignored by both device 1 and device 2 because it will be considered by them to be outside of their subnet.
IP subnet that is masked by 255.255.255.0 will only be capable of supporting 256 devices. This is known as a class C subnet.
IP subnet that is masked by 255.255.0.0 will be capable of supporting 65,536 devices. This is known as a class B subnet.
In most situations, including home or small office network, a class C subnet is more than enough.
After confining devices and their broadcasts within a subnet, there needs to be a way for them to access the outside world, for example, to the world wide web. A gateway is needed for this purpose. A gateway is a logical term or concept. The physical device that serves as a gateway is usually a computer or a router.
The Default Gateway is often part of a device’s IP network setting to indicate where all outbound IP messages should go. The gateway device will then take those messages and resend it to the outside world. Since it is a device on the IP network, a gateway device also has an IP address. The Default Gateway is therefore also composed of 4 groups or numbers separated by periods. And it should also be part of the subnet of the devices.
If you have broadband Internet access (usually cable or DSL), one of the most common ways to connect your devices is through a router.
Disgram: IP Network Example
Notice that the router has 2 IP addresses. One is inward-facing. That is its IP address to the rest of the internal network. The other is outward-facing. That is its IP address to the rest of the Internet.
Dynamic Host Configuration Protocol (DHCP) is a way for a device on a network to automatically assign IP addresses to other devices. DHCP requires that one of the devices on the network to be the DHCP host. When other devices are turned on and want to become part of the network, it will send out (broadcast) a DHCP request. While the message is ignored by other non-DHCP-host devices, the DHCP host device will process the request and return the IP address that the requesting device should use for the duration.
In simple home networking, the router is most likely also acting as a DHCP host.
Besides, IP address, subnet mask, and default gateway, DHCP is also responsible for passing along other information such as the addresses for domain name servers (DNS) to the requesting devices.
** DNS is what translates www.MS.com into 188.8.131.52 or www.xbox-scene.com to 184.108.40.206 **