DAN - Network Communication (Lesson)

Network Communication

Introduction

In this lesson, you will learn how network devices are identified as well as explore the network communication process.

Humans typically communicate using two basic methods:

  1. Speaking: in person, in a group, on the phone, etc.
  2. Writing: letter, email, text message, notes on the board, etc.

The typical methods have rules to make it work smoothly:

  1. Speaking: Take turns, raise your hand, no yelling, etc.
  2. Writing: Proper format, punctuation, etc.

Network communications have rules, too! The typical rules are:

  • Rules for finding devices on the network.
  • Rules for making connections.
  • Rules for each type of information being shared.

Human beings developed methods for ensuring that our communications are not chaotic and people are not screaming on top of each other to be heard. This is why we have rules for taking turns, for specifying who we are talking to, etc. Network communications have rules, too – and they are actually similar to human communication rules!

Here is a short animation of finding devices on the network:

Finding Devices on a Network Animation

The first job in networking is to find the device we want to communicate with by exchanging data.  In a crowded room, how would Harry find Sally? He could just yell her name, right? What if there are five Sallys in the room? How would Harry know his yelled message is getting to the right Sally?  The same thing is true in a network, except maybe worse -- because we can’t actually deliver data based on the name of the user sitting at the computer!  We need a very specific way of addressing data packets so that no delivery mistakes are made.

Finding Devices on the Network Rules

Rule #1

Your device must be unique! There must be an addressing system as a way of uniquely identifying computer interfaces. By the way, an “interface” on a device is a component that acts as a door for connections. There are many Sallys in the world but only one unique Meg Ryan who plays Sally in the 1989 “When Harry Met Sally” movie.

We already briefly mentioned the NIC in a previous lesson but here is a quick review: NIC stands for a Network Interface Card. Every NIC has a hardcoded Media Access Control (MAC) Address assigned by the manufacturer. MAC Address is also known as the physical address of a device. It is represented as 12 hexadecimal digits: 00:24:E8:83:68:96 or 00-C0-CA-52-38-8C.

Devices can have more than one NIC but each one MUST have its own unique MAC address. MAC addresses are hard for humans to remember and organize. Sort of like trying to find a person by using their fingerprint.

Since these MAC addresses are unique, that means that devices can communicate reliably across large networks. As long as they remain secure… just like our Social Security number, passport number, etc. MAC address spoofing is often used to bypass Wi-Fi security features.

Rule #2

You must “belong” to a network! Joining a network provides you with lots of cool stuff, such as access to shared files, devices like printers or scanners, Internet Service Providers, etc. When you join a network, you become connected!

We actually use a second address in networking, not just the MAC address.  While MAC addresses are unique, the hexadecimal numbers are difficult for humans to work with and remember.  Plus, since they are burned into the ROM, we can’t manipulate them to help with organizing. MAC addresses are a lot like fingerprints -- they are unique, for sure, but not exactly an easy way to look someone up to say, “Hi!”

Network and IP Address Video

To join the network, you get an Internet Protocol (IP) Address! It is a temporary identifier for each interface and must be unique among the connected devices on that network. It is also known as the logical address of a device.

An IP address is similar to a phone number because it is easy to remember, write down, and look up. You can also change your IP address, based on what network you are on at the time.

It is important to emphasize that an IP address still must be within your local area network. If you are at school, your laptop gets an IP address that is unique from all the other PCs on the school network. However, when you go home and sit down to work on your school assignments, your laptop gets a new IP address that is unique from all the ones on the home network.

Practice Activity

Google "what is my IP address" and use one of the free websites to look up your current IP address.  For example, What is My IP Address."

Did you notice two different types of IP addresses? IPv4 is the old kind, but it is still the most commonly used. IPv6 is newer but not yet widely used.

IPv4 to IPv6 Transition

The IPV4 format is four decimal numbers separated by dots (dotted decimal notation). Each section is called an octet (because it holds 8 bits) and can hold a decimal number from 0 to 255, meaning that If each bit is turned on, then that binary number (11111111) will equal 255.  Example: 192.168.55.32

The transition from IPv4 to IPv6 is primarily driven by the depletion of IPv4 addresses and the need for a more secure, efficient, and scalable Internet addressing system.

Here are the key reasons for this transition:

  • IPv4 Address Exhaustion: IPv4 uses a 32-bit addressing scheme, which allows for approximately 4.3 billion unique addresses. With the explosive growth of the Internet and the increasing number of devices connecting online, including smartphones, tablets, and IoT (Internet of Things) devices, the pool of available IPv4 addresses has been depleted. IPv6, with its 128-bit addressing, provides a virtually limitless number of IP addresses, solving the problem of address exhaustion.
  • Simplified Network Configuration: IPv6 includes features that simplify aspects of network configuration, such as address auto-configuration (including stateless address autoconfiguration or SLAAC), which reduces the need for manual configuration of IP addresses and can simplify network administration.
  • Improved Security: IPv6 was designed with security in mind. It includes IPsec (a suite of protocols for securing internet protocol communications) as a fundamental feature, which provides a more secure communication channel compared to IPv4, where IPsec is optional.
  • Enhanced Efficiency: IPv6 improves upon IPv4 in several ways that enhance the efficiency of data routing and packet processing. For example, IPv6 headers are simpler and more efficiently processed by routers. It also supports multicasting more effectively, allowing for the efficient distribution of data to multiple destinations.

The transition from IPv4 to IPv6 is a gradual process because it requires significant changes to the Internet's infrastructure. Many devices and systems need to be upgraded or configured to support IPv6, and both protocols will continue to coexist for some time through various transition mechanisms, such as dual-stack configurations, where systems run both IPv4 and IPv6 simultaneously.

Rule #3

The sending device must know BOTH the IP and the MAC address of the receiving device. Address Resolution Protocol (ARP) is a tool used by devices on the same network to find the MAC address associated with an IP address. ARP is a foundation of network communications. It is exactly like someone yelling in a room to find someone else. One device broadcasts an ARP request to all the devices on the network.  It’s sort of like yelling to see if you can find someone. The device with the IP address responds with its MAC address.  If a network has a lot of ARP broadcasts going out, then that network is probably going slow. Just like when highways slow down when they have too much volume, the same is true of networks.

Here is a short animation of how ARP works:

How ARP Works Animation

Bob wants to send a message to a computer whose IP address is 10.0.0.1 BUT he needs the MAC address for that device. Remember, a device can’t send packets to a specific device unless we have both the IP and the MAC address!

Bob sends out an ARP broadcast, a message that goes to every connected computer asking, “Who is 10.0.0.1?” Sally’s computer responds by providing her MAC address. Bob puts that information in his ARP table so that any further packets for Sally can go right out without the need for more ARP broadcasts. Please note that the ARP table doesn’t last forever because devices don’t keep their IP addresses forever.

Practice Activity

  1. On a computer connected to a network, open the command prompt:
    1. Click on the Start button or press the Windows key on your keyboard.
    2. Type "cmd" or "Command Prompt" into the search bar.
    3. Click on the Command Prompt app from the search results to open it.
  2. Type arp -a (note space between arp and -a) and press Enter to display the ARP table.
  3. Observe the IP and MAC addresses listed.

Reflection and Wrap-up

In this lesson, you have learned how network devices are uniquely identified and communicate with each other using specific rules and protocols. Through the concepts of MAC and IP addresses and the Address Resolution Protocol (ARP), you have explored the foundational aspects of network communication which ensures that your devices can reliably connect and share information in a structured and efficient manner.

[CC BY-NC-SA 4.0 Links to an external site.] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION - INTENDED ONLY FOR USE WITHIN LESSON.