Internet Protocol (“IP”) Address

The third layer of the TCP/IP (the IP Layer) is the most important to us so we will spend a lot of time on this specific subject. We’ll start with the concept of using an IP address to create a fully functional network over the IP address technology.

To make our study of IP easier, you should know the following facts about it:

1. All devices on the network must have an IP address assigned to communicate.
2. All devices on the network must have a unique IP address assigned; two or more devices cannot share the same IP address. If two devices are assigned the same IP address, neither of them will be able to communicate on the network.
3. The current versions of IP addresses in TCP/IP networks today belong to IP V4 and IP V6.
4. IP V.4 is much popular than IPV6, and will be for a long time due to its ease of addressing (we’ll talk more about this later).

• For each IP address assigned to a device, there is a subnet mask associated with it. The subnet mask identifies the network and host IDs.
• If a device tries to locate another device at a different IP address segment of the network, it needs to contact a default gateway to process that request. Default gateways aren’t primary components of IP addresses and can be avoided as long as we want to stay within our network.

In this example we will simulate the five facts we just mentioned about IP addressing.

1. All devices on the network must have an IP address assigned to communicate: I live in Alexandria, VA, where the area code is 703. We will assume that the IP address is represented by the local phone number for all people who live in the Alexandria area. So if my phone number is 111-1111 and my wife’s phone number is 222-2222, she and I will be able to communicate by dialling either 111-1111 from her phone or 222-2222 from my phone. I won’t be able to reach my wife if she has a phone without a phone number assigned to her, and that is the case for each individual with a phone. Each one must have a phone number in order for them to be able to communicate with others through the phone.
2. All devices on the network must have a unique IP address assigned; two or more devices cannot share the same IP address. If two devices were assigned the same IP address, neither of them would be able to communicate on the network properly: No two phones can have the same phone number. The only way that this

could happen is if the phone company assigned a phone number to two people with two different extensions. So if both Mike and Faith have the phone number 703-111- 1111, when someone calls the automated system will answer and will ask the person calling to enter the extension number of the person he wants to reach. Mike and Faith must have different extensions in order for anyone to be able to contact them.

3          The current versions of IP addresses in TCP/IP Networks today are IPv4 and IPv6

IPv4 is much popular than IPv6, and will be for a long time due to its ease of addressing and management : In the US we have 10-digit phone numbers, which include the area code and phone number. The area code consists of three digits and the phone number consists of seven. Other countries like India have a different format of numbers than us, due to a larger population (380 million in the US versus 1.4 billion in India). The Indian government needs more digits to cover the increased demand on the phone service.

The same thing is applicable to IP addresses. We still have addresses available, but that won’t be the case in a few decades or even years. Internet growth is insanely fast and the more websites that exist, the more IP addresses we need to cover the high demand and other services that use IP. This is why IP developers came up with IP V.6. IP V.6 has so many addresses that I can’t even say the number. Some say that IP V.6 has enough addresses to give each living creature on this planet an IP address without running out.

IPv4 and IPv6 It comes installed by default on Windows 10/11 and Windows Server 2012/2019/2022. We will cover IP V.6 later on.

• For each IP address assigned to a device, there is a subnet mask associated with it. The subnet mask identifies the network host IDs: When you dial a local number in Alexandria or anywhere else, you don’t need to enter the area code. All you need to do is dial the seven-digit number and the phone service will assume that the number you’re dialling is local. The same thing is applicable with IP addresses. When two machines try to connect to each other, the first machine checks to see if the other machine is located on the same network. If it is, then the first machine tries to connect to the second directly without using a router (analogous to an area code of a different city). If Machine B exists on another network, Machine A connects to a router that

will establish connection to the destination router of Machine B’s network, where that router will transfer the data to the final destination. The answer to the question of how the machine determines whether the other machine it’s trying to connect to is local (i.e., on the same network) or foreign (i.e., on a different network) lies in the subnet mask. For now, all you need to know is that the subnet mask is one of the components that determine whether the remote machine’s IP address is local or foreign. We will discuss the subnet mask later.

• If a device tries to locate another device on a different IP address segment of the network, it needs to contact a default gateway to process that request. Default gateways aren’t primary components of IP addresses and can be avoided as long as we want to stay within our network: I live in Alexandria and if I want to call someone who lives outside of the Alexandria area, I need to enter the area code along with the phone number. For instance, if I want to call Seattle, I need to enter the Area Code 206 followed by the person’s phone number. The area code is the sequence that determines where my call is directed, and routes my call over to the destination. Applying this rule on the network, the area code is represented by a “router” device. A router carries data from your local network to another network with a different network ID. If you have multiple devices on the same network in your house or at work, you won’t need to have a router to connect these devices together. The only time you will need a router is when you want traffic to travel outside of your network to another network. Shortly, we will see an example where a router is used as a network communication device based on the IP protocol.

Subnet Mask

A subnet mask was created to identify two major portions of the network: the network ID and the host ID. The network ID identifies the digits that belong to the network. Those digits aren’t changeable; in order for a client to belong to a network, the client must have the same network ID. The host ID is the group of digits dedicated to hosts on a network. Each host must have the same network ID and a different host ID to be able to communicate on the network. Subnet masks, like IP addresses, have the same format: four fields separated by dots and numbered from 0-255; for example:

255.0.0.0

255.255.255.128

255.255.0.0

255.255.255.255

Example 1

We will take an example with the subnet mask 255.255.0.0 and see how that subnet mask can be associated with an IP address. As we move on, we will learn more about subnet mask addressing along with IP addresses. We will start with a network that consists of two computers (Host A, IP address 10.1.1.1, and Host B, IP address 10.1.1.254); both have the same subnet mask so they can connect with each other.

Figure 1.             Host A and Host B

With a subnet mask of 255.255.0.0 these two hosts can communicate without any problem because the subnet mask starts with the field value 255. For every IP address field, there is a corresponding subnet mask field. For instance, the host A IP address will correspond to the subnet mask as follows:

IP Address:	10	1	1	1
Subnet Mask:	255	255	0	0

When a subnet mask contains the value 255 in any of its fields, it means that the corresponding IP field for all hosts on the network has to be static. This is how subnet masks tell you “sorry buddy, this value is reserved and cannot be changed”. Applying that rule in our example above, we see that we cannot change the IP address’ first two fields.

The number 0 in the subnet mask means that we can change the corresponding IP address field to any value from 0-255. Applying that rule to our example, along with the first rule, we come to the conclusion that Host A can have any IP address from the range of

10 .1.0.0-10.1./255.255.0.0

The network ID is represented by the digits that must be the same on every host on the network, while the host ID can be changed for each client. In our previous example, the network ID was the first two fields of the IP address (10.1), and the host ID was represented by the last two fields of the IP address (1.1). How did we know that? Here is how: going back to the IP address and subnet mask of Host A, we will have:

IP Address:	10	1	1	1
Subnet Mask:	255	255	0	0

1. All computers on a network with the subnet mask 255.255.0.0 will share the first two fields of the IP address, which means that all computers IP addresses on that network will start with (10.1) (this is the network ID).
2. Now determining the Host ID couldn’t be easier. The host ID is obviously represented by the rest of the subnet mask’s unused fields. The host ID for our network is the last two fields of the IP address.

Figure 2.             Network and Host IDs

Subnet masks help us a lot in dividing our IP network into multiple hosts and networks so we’ll go over a couple more examples.

Example 2

There are two host computers, A and B.

Table 1-4.              Host A and Host B’s IP Addresses and Subnet Masks

Host	IP Address	Subnet Mask
A	192.168.2.5	255.255.255.0
B	192.168.1.5	255.255.255.0

Will Host A be able to communicate with Host B?

Let’s start the solution with our two-step procedure of the network and the host ID.

Host A

Figure 3.           Host A’s IP address and subnet mask information

• The subnet mask includes three fields that hold the value 255, so none of the corresponding IP address fields will change. Therefore, the first three fields of Host A’s IP address are reserved for the network ID, which is 192.168.2.0.
• The subnet mask’s last field value is 0, which means that a host can have any value from 0-255. (Theoretically anyway; technically, we can have any value from 1-254. The values 0 and 255 are reserved for other purposes as we will see later.)

Host B

Figure 4.           Host B’s IP address and subnet mask information

• The subnet mask includes three fields that hold the value 255 so none of the corresponding IP address fields will change. Therefore, the first three fields of Host A’s IP address are reserved for the network ID, which is 192.168.1.0.
• The subnet mask’s last field value is 0, which means that a host can have any value from 0-255.

Compare both network IDs; if they are identical, then they can communicate directly without a router. If not, they will need a router to communicate.

Host A’s network ID is 192.168.2.0 and Host B’s network ID is 192.168.1.0. Can they communicate? No, because all three fields aren’t identical; you will need a routing device to route information between both networks. Keep the following information in mind:

1. If you have two devices with an identical Network ID and different host IDs, they will be able to communicate without any problem.
2. If you have two devices with different Network IDs, you will need a router for those networks to be able to communicate.
3. If you have two devices with the same Network ID and the same Host ID, they will not be able to communicate with one another.

Example 3

There are two host computers, A and B.

Table 1-5.              Host A and B IP and Subnet Mask Addresses

Host	IP address	Subnet Mask
A	10.100.2.154	255.255.128.0
B	10.200.5.199	255.255.252.0

Will host A be able to communicate with host B?

No, because the first two fields of the IP address are not the same.