Chapter 3: IP Addressing and Subnetting

The internet acts as an enormous digital world, and it's continuously expanding with new users and internet-connected devices coming online every day. Every device on a network requires some type of address to be able to communicate and exchange messages. To meet this need, Internet Protocol (IP) addresses are commonly used.

Throughout this chapter, you will learn about the characteristics of both IPv4 and IPv6 addressing schemes, while discovering the various types of transmissions that occur on a network, as well as the importance of subnet masks and the role they play in a network.

In this chapter, we will cover the following topics:

• The need for IP addressing
• Characteristics of IPv4
• Classes of IPv4 addresses
• Special IPv4 addresses
• Subnet mask
• Subnetting
• IPv6
• Lab – Configuring IPv6 addresses on a Cisco device
• Lab – Configuring IPv6 addresses on a Windows computer
• Testing...

Technical requirements

To follow along with the exercises in this chapter, please ensure that you meet the following hardware and software requirements:

• Cisco Packet Tracer
• GNS3
• GNS3 VM
• Configuration files: https://github.com/PacktPublishing/Implementing-and-Administering-Cisco-Solutions/tree/master/Chapter%2003

Check out the following video to see the Code in Action: https://bit.ly/3iQDXZT

The need for IP addressing

A computer network is a bit like a neighborhood or community. Communities consist of many people, houses, schools, and businesses. Each of these houses and buildings has a postal (mailing) address that allows others to send letters and packages via a courier service to the recipients. Without a mailing or postal address, it's a bit challenging for others to send a physical letter or package to you. Similarly, on a computer network, each device has a unique address that is used for sending and receiving messages (signals) between them. These addresses are known as Internet Protocol addresses and are most commonly referred to as IP addresses.

How do we know which IP addresses can be used on the internet and on private networks? There is a special organization that manages both IPv4 and IPv6 addresses. This organization is known as the Internet Assigned Numbers Authority (IANA). The IANA is also responsible for governing the usage of the Domain Name...

Characteristics of IPv4

Learning about computer networking is always a fascinating topic as it also introduces you to how computing devices interpret data and present information. Using a computer or smart device, we usually see a very well-polished graphical user interface (GUI). In Microsoft Windows, for example, there is Windows Explorer, which helps us navigate the various areas (locations) of a computer easily. When opening files, such as pictures, the photo viewer application presents us with a picture our minds can interpret. However, by default, computers and networking devices are unable to interpret the objects within a picture.

When data is written onto a hard disk drive (HDD), there's an actuator arm that contains a read/write head (pin), which is used to magnetize and de-magnetize areas on the platters to represent data. This means that what we see as a picture of a car on the computer screen is, to the device, a portion of the HDD being magnetized and de-magnetized...

Classes of IPv4 addresses

Who determines which IPv4 address can be assigned to our internal devices, and those that are directly connected to, or facing, the internet? When the Internet Assigned Numbers Authority (IANA) became entrusted with the management of IP addresses, a portion of IPv4 addresses were made to be used on the internet and on the devices that are directly connected to the internet. Meanwhile, another portion was assigned to be strictly usable only on internal networks, such as a home network or within an organization.

In IPv4, there are two address spaces. These are as follows:

• Public IPv4 address space
• Private IPv4 address space

In the following sections, we will discuss each address spaces in further detail, describing the characteristics and uses of both public and private IP addresses.

Public IPv4 address space

We will first discuss the characteristics of the public IPv4 space. IANA has divided IP addresses into five classes. Each...

Special IPv4 addresses

In the IPv4 address space, there are three special network blocks that are reserved for special usage. These special IPv4 addresses are as follows:

• Loopback address
• Test-Net
• Link Local

In this section, we will look at each of their characteristics and use cases.

Loopback address

The loopback range of an address is built into the TCP/IP protocol suite. This range of addresses allows an application running on a host machine to communicate with an application on the same machine. To put it more simply, loopback addresses allow a host operating system to send network traffic to itself.

The network block is reserved for loopback and has the range 127.0.0.1/8 to 127.255.255.254/8. Therefore, to test the functionality of the TCP/IP protocol suite, you ping any address from the loopback range. Most commonly, network professionals ping the 127.0.0.1 address.

Test-Net

According to RFC 3330, the block of addresses 192.0.2.0/24 to...

Subnet mask

An IP address is not complete without being associated with a subnet (work) mask. The subnet mask has the following characteristics and responsibilities on a network:

• IPv4 subnet masks are 32 bits in length, while IPv6 subnet masks are 128 bits.
• A subnet mask is used to identify both the network and host portions of an IP address.
• A subnet mask is used to assist us and network devices in determining the total number of networks, as well as the total usable IP addresses that exist on an IP subnet.
• The subnet mask is used to help a host device determine whether a packet should be sent to the default gateway if the intended destination is beyond the local network.

As we have learned in the previous sections, there are typically three classes (A, B, and C) of assignable IP addresses for both public and private address spaces. Similarly, there are three default subnet masks for each class of IPv4 address.

The following are the three default subnet...

Subnetting

Hearing the word subnetting can be a bit intimidating when learning a networking-related certification. However, learning subnetting is unavoidable on your journey to becoming an awesome network engineer. You may be wondering, what is subnetting and why do we need to learn how to perform this task as a networking professional? To get a better understanding of the answer to this question, let's use a simple analogy. Let's imagine you are the network administrator at a company that has 6 networks, and each of these networks has no more than 50 devices that require an IP address.

It would be easy to simply take a Class C network block such as 192.168.1.0/24 and assign it to the network, then choose another Class C address block to assign to the next network, and so on. The following is a typical workable solution for assigning network blocks to the 6 networks:

• Network 1: 192.168.1.0/24
• Network 2: 192.168.2.0/24
• Network 3: 192.168.3.0/24
• Network...

IPv6

The need for IPv6 is ever-demanding on the internet today, with the creation of new smart and Internet of Things (IoT) technologies causing an exhaustion of the public IPv4 address space quicker than expected. Nowadays, a typical person may have more than one smart device in their household, from internet-connected appliances to home security systems. The need for internet connectivity is an ever-increasing demand, hence the creation of a new address space.

The following is a brief summary of IPv4 exhaustion statistics:

• APNIC: Exhausted in April 2011
• RIPE NCC: Exhausted in September 2012
• LACNIC: Exhausted in June 2014
• ARIN: Exhausted in July 2015
• AfriNIC: Expected to be exhausted in 2019

This is where IP version 6 comes in. Back in December 1995 (circa), the IANA was entrusted to manage the IPv6 addressing scheme (RFC 1881). This means that IPv6 was developed and ready for distribution a long time ago. IANA, RIRs, and AS were waiting for the last...

Lab – Configuring IPv6 on a Cisco IOS router

To get started, we are going to use the following topology:

Fig 3.48 – Lab topology

To configure IPv6 address on a Cisco IOS router, use the following steps:

1. Enable IPv6 routing using the following command:

   R1(config)#ipv6 unicast-routing

2. Enter interface mode for the desired interface:

   R1(config)#interface GigabitEthernet0/0

3. Use the ipv6 address command, followed by the IPv6 address with the network prefix:

   R1(config-if)#ipv6 address 2001:DB8:1:1::1/64

4. (Optional) To manually configure a Link-Local IPv6 address on the interface, use the link-local command after the IPv6 address, as shown here:

   R1(config-if)#ipv6 address FE80::1 link-local

5. Enable the interface using the no shutdown command:

   R1(config-if)#no shutdown

Now that you have learned how to configure IPv6 global and Link-Local addresses, let's take a look at how to verify our configurations using Cisco IOS commands...

Lab – Configuring IPv6 on a Windows computer

Now that you have learned how to manually configure an IPv6 address on a Cisco router, let's take a look at how to manually configure an IPv6 address on a Microsoft Windows computer.

To get started with this task, use the following steps:

1. Open the Windows Control Panel and go to Network and Sharing Center.
2. On the left, click on Change adapter settings.
3. Right-click on your corresponding network adapter and select Properties.
4. Click on Internet Protocol version 6 (TCP/IPv6) and then click on Properties:

   Figure 3.52 – Network adapter properties

5. Use the following setting to assign the IPv6 address, network prefix, and default gateway configurations to the PC:

   Figure 3.53 – IPv6 settings on PC

   The DNS server settings can be adjusted to your preference. I am using a Cloudflare IPv6 DNS server as my DNS server.

6. Click OK to save your settings.
7. To check your configurations, open the Command...

Testing end-to-end connectivity

After configuring and verifying your IPv6 configurations, the last thing a professional must always do is test end-to-end network connectivity between devices.

On our router, let's test the connection between the router and the computer on our topology using the ping command:

Figure 3.54 – Ping results on Cisco IOS

As you can see, we got five exclamation marks (!). This means we have successful replies from the PC. Receiving a dot (.) means Request Timeout, while U means destination unreachable on the Cisco IOS. If you are not getting a successful connection, double-check your configurations and ensure the cables are connected to the configured interfaces on each device.

Summary

Throughout this chapter, we have covered the essentials for understanding both the IPv4 and IPv6 address spaces, demonstrated how to convert an IP address into binary, determined the Network ID of devices, and learned about the various types of network transmissions.

You also learned how to identify each class of IP address, how to perform subnetting, how to describe the characteristics of both IPv4 and IPv6, and how to configure and verify interfaces on a Cisco device.

I hope this chapter has been informative for you and has been helpful in your journey toward learning how to implement and administer Cisco solutions, in preparation for the CCNA 200-301 certification. In the next chapter, Wireless Architectures and Virtualization, we will learn about Cisco wireless architectures and virtualization technologies.

Further reading

The following links are recommended for additional reading:

• IP addressing and subnetting: https://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13788-3.html
• Configuring IPv4: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_ipv4/configuration/xe-3s/ipv4-xe-3s-book/configuring_ipv4_addresses.html
• IPv6 addressing and connectivity: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipv6_basic/configuration/xe-3s/ip6b-xe-3s-book/ip6-add-basic-conn-xe.html
• Implementing IPv6 addressing: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipv6/configuration/15-2mt/ipv6-15-2mt-book/ip6-addrg-bsc-con.html