4.1 The Internet

IP Address

What is an IP Address: A numeric label assigned to every device that uses the internet to communicate. IP stands for Internet Protocol. IP addresses are the identifiers that allow data to be sent over the internet.

contain location information
allows devices to communicate over internet
differentiates between computers, routers, and websites

A set of 4 8-bit numbers seperated by periods. Each number is in the range 0-255. Exceptions are 0.0.0.0 and 255.255.255.255

4.20.0.255
16.23.234.1

ipaddresstypes

IP Addresses allow us to send information in three main ways.

Unicast - a specific device. Internet wide access. TCP is used
Multicast - a group of devices. It is specific range of IP addresses. Internet-wide access. UDP is used
Broadcast - all devices. LAN-wide. Data stops at the router. UDP is used

Popcorn Hack - Finding your IP

https://www.whatsmyip.org/ works for both mac and windows

Alternatively, you can open up a command prompt (cmd into search bar), and type ipconfig

The OSI Model and TCP/IP Model

TCP/IP Protocols

A TCP/IP Protocol is a set of rules that governs something within computer communication. The IETF, or Internet Engineering Task Force, manages these rules and facilitates the open development of them.

Example: ASCII Protocol

ASCII (American Standard Code for Information Interchange) is a internet protocol that you may be familiar with, is a type of character encoding

ASCII is a protocol governing how text is represented as binary

128 characters, 95 printable

There are many more protocols, each governing a specific area of how computer communicate. Ex. ARP, DNS, FTP, UDP, PPP, SAP

We obviously can’t cover every protocol, but we’ll be talking about a few important ones today.

OSI Model

The OSI model, also known as the Open Systems Interconnection Model, helps represent communications between two computers.

The OSI model helps coordinate and classify standards
Each of the many protocols can be classified into one of the seven layers
Each layer has a function and the protocols in that layer all help with that function

Layer	Name	Function	Example
1	Physical	Transport of data between tangible, physical things	DSL
2	Data Link	Device identification and forwarding on a LOCAL network (i.e. home, school)	PPP
3	Network	Manages identification and path that a device should take, very few of these protocols	STP
4	Transport	Manages transport of data between computers (delivery method, i.e. fast vs slow)	UDP
5	Session	Manages connectivity between devices	SAP
6	Presentation	Translates from data sent between computers (binary) to something humans can understand	TLS
7	Application	User Interaction, like resource sharing	HTTP

Popcorn Hack

We just gave an example of a protocol, ASCII, above. What OSI Layer does ASCII fall into?

Give another example of a protocol from that layer

TCP/IP Model

Another method of classifying protocols
Simplifies OSI model into four layers
Application, Presentation, Session layers are summarised into one Application layer
Data Link and Physical layers and summarised into one Link or Physical layer
This layer, also known as Network Access, is focused on the transport of bits (1s and 0s) between networks

Protocols

DNS - Domain Name Service

DNS, or Domain Name Service, is a naming system for websites on the internet.
DNS assigns and has records that relate domain names to ip addresses

What is a Domain Name?

Domain Names are strings used to identify addresses
They map hard to remember IP addresses into simple string of text
Would you rather remember 162.159.128.233 or discord.com?
Each website has its own IP address that you are sent to when you visit the website
https://www.nslookup.io/website-to-ip-lookup/
nslookup (website) in command prompt

Popcorn Hack

Open up a command prompt and type “nslookup google.com”

You should get 142.250.68.78, we mainly care about the bottom address for now

Try visiting that website in your search bar!

Subdomains

Subdomains are a prefix added to a domain to separate parts of the website
There can many subdomains, up to 127, and each can be up to 64 characters long
We saw an example of this in our passion projects
(SUBDOMAIN).stu.nighthawkcodingsociety.com

Domain Name Service Providers

DNS Providers manage and sell domain names

Popcorn Hack

List 4 more websites you use often and their IPs

What’s a subdomain of your passion project backend from last time?

What’s the domain of your current binary CPT project?

HTTP vs HTTPS - HyperText Transfer Protocol

HTTP (Hypertext Transfer Protocol) and HTTPS (Hypertext Transfer Protocol Secure) are both protocols used for transferring data over the web. The key difference lies in the security aspect.

HTTP is the standard protocol for transmitting data over the internet. However, it does not provide any encryption, making it susceptible to eavesdropping and unauthorized access. This means that any information exchanged between the user’s browser and the website, such as login credentials or personal data, is sent in plain text.

HTTPS

On the other hand, HTTPS adds a layer of security by incorporating SSL/TLS (Secure Sockets Layer/Transport Layer Security) encryption. This encryption ensures that the data exchanged between the user and the website is encrypted, making it much more challenging for malicious actors to intercept or tamper with the information.

We SSL based encryption last trimester with certbot. Certbot generated SSL certificates for us to ensure HTTPS connection between the client and your website.

TCP and UDP - Transmission Control Protocol and User Datagram Protocol

TCP and UDP are both Transport protocols (layer 4 of OSI and layer 3 of TCP/IP). This means they are a set of rules that specify how data is exchanged between devices over the Internet.

TCP Packets

What’s in a TCP packet? Packets are a unit of information that are sent over the network. They contain user data, among other identification information.

TCP Handshake

The TCP handshake process - this is how a TCP session is initiated.

Step 1: Client A requests a client-to-server communication session with Server B (SYN)

Step 2: Server B acknowledges client-to-server communication session, requests server-to-client communication session (SYN-ACK)

Step 3: Client A acknowledges server-to-client communication session (ACK)

After these steps are executed in order, the communication pathway is established between Client A and Server B.

How does TCP actually send the data?

Client A wants to send some file to Server B. TCP will first split the data into 6 segments
TCP forwards the first 3 segments to the Server B
Server B must acknowledge that it has received the segments by sending back an ACK. If Client A doesn’t receive the ACK, it resends the segments
Client A sends the remaining 3 segments
Again, Server B must send back an ACK to confirm it has received the other 3 segments

TCP Session Termination

Client A sends segment to server B with the FIN flag to terminate the client-to-server session
Server B sends ACK to client A
Server B sends FIN to client A to terminate the server-to-client session
Client A sends ACK to server B
The session closes

UDP

Enough about TCP… what about UDP?

UDP Pros:

Little cost
Faster

UDP Cons:

Little data checking
Generally unreliable, as no ACK messages are sent
Packets may arrive out of order or have duplicates/missing packets

UDP sends out all packets at once without any form of handshake or acknowledgement.

Popcorn Hack

When do we use UDP? While it seems terrible, try to think of some use cases!

When might we use TCP?

Homework Questions

Please answer all of these questions on your personal blog and explain. Don’t just give an answer. Homework is due Sunday night at 6 pm

IP Addresses

Which of the following IP Addresses are possible? Explain (yes/no) for each answer choice.
1.1.1.1.1: No. This is not a valid IPv4 address. IPv4 addresses consist of four octets, each ranging from 0 to 255.

23.23.23.23: Yes. This is a valid IPv4 address. Each octet is within the range of 0 to 255.

134.492.100.0: No. This is not a valid IPv4 address. The second octet exceeds 255.

255.256.55.255: No. This is not a valid IPv4 address. The second octet exceeds 255.

2.93.255.19: Yes. This is a valid IPv4 address. Each octet is within the range of 0 to 255.

If Dian Du is at home on his home network and sends a message to every computer on the network, what is this an example of? Explain.

If Dian Du sends a message to every computer on his home network, it is an example of broadcast. In networking, broadcast refers to a communication method where a message is sent from one sender to all possible recipients within the network. It is a one-to-all communication model. In a broadcast, the message is addressed to a special broadcast address that signifies all devices on the network

Models

Three of the four following protocols are on the same layer. Identify which ones and what layer they are on, and why they are on each layer: FTP and TLS are on the Application Layer (Layer 7) because they provide application-level services related to file transfer and security.
Telnet is a internet protocol which allows remote access to other computers over a local network or the internet. What layer of the OSI model would this protocol be located on? What is the function of this layer? Telnet operates at the Application Layer (Layer 7) of the OSI model. This layer provides network services directly to end-users or applications. Telnet enables remote access to other computers over a network, allowing users to log in and control remote systems.

DNS

Bob wants to use the domain bob.is.the.best.com. What domain should he buy from a DNS provider (assume it is available)? What would be the subdomains?

If Bob wants to use the domain “bob.is.the.best.com,” he should purchase the domain “best.com” from a DNS provider. In this case:

Main Domain (Second-Level Domain): “best.com” Subdomains: “bob.is.the” So, “bob.is.the.best.com” breaks down as follows:

Main Domain (Second-Level Domain): “best.com” Subdomains: “bob”, “is”, “the” Bob would need to register “best.com” and then configure the appropriate subdomains within his DNS settings if he wants to use subdomains like “bob.is.the.best.com.”

HTTP and HTTPS

What is a difference between HTTP and HTTPS?

while both HTTP and HTTPS are protocols for transmitting data over the internet, HTTPS adds a layer of security by encrypting the communication, making it more secure and suitable for transmitting sensitive information such as login credentials, personal data, and financial transactions.

Last trimester we sent HTTP requests for our passion projects
- Did we use HTTP or HTTPS? Yes
- What are the benefits and disadvantages of this? They can transmit data over the internet quickly.

TCP and UDP

Bob is setting up a video streaming service, and he needs the stream to be real time.
- What protocol should he use, TCP or UDP? Why?

Bob should use UDP (User Datagram Protocol) for his real-time video streaming service. UDP’s lower latency and lack of retransmission make it more suitable for real-time applications, ensuring a smoother and more immediate viewing experience compared to TCP.

What are some cons of this protocol? Give an example of a potential issue. Cons of UDP:

No guaranteed delivery. No order guarantee. No flow control. Limited error checking. Not suitable for applications requiring reliable and ordered data delivery.

TCP has error checking, which ensures that all packets arrive properly. Why is this important?
- Give an example of how TCP ensures that there are no errors. TCP ensures error-free communication through acknowledgments (ACKs) and retransmission. When a sender sends data, it expects acknowledgments from the receiver. If not received, the sender retransmits the data until acknowledged, ensuring reliable delivery.
Server A computer is communicating with Server B. They have already initiated communication and Server A is now attempting to send data to Server B.
- How does Server B ensure that they have received any sent packets before Server A continues sending packets in TCP? In UDP? TCP: Server B ensures packet reception by sending acknowledgments (ACKs) to Server A. If no ACK is received, Server A retransmits.

UDP: In UDP, there’s no automatic acknowledgment. Server A must implement its own acknowledgment mechanism if needed.

What is another use of this? Acknowledgment mechanisms, as found in protocols like TCP, are also used in file transfers, messaging systems, and remote procedure calls to ensure reliable and ordered communication in various networked applications.

4.1 - The Internet

Internet and basic protocols

4.1 - The Internet • 33 min read

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