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.

  1. Unicast - a specific device. Internet wide access. TCP is used
  2. Multicast - a group of devices. It is specific range of IP addresses. Internet-wide access. UDP is used
  3. 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
  • My IP (school IP): 209.66.205.197

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
  • ASCII is in the presentation layer. Another example is TLS

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?
  • Youtube (142.251.40.46), Instagram (31.13.70.174), TikTok (18.65.25.51), Krunker (50.87.195.134)
  • /Asian-United-Fronted/
  • N/A

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.

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

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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.

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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)

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

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

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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?

  1. Client A wants to send some file to Server B. TCP will first split the data into 6 segments
  2. TCP forwards the first 3 segments to the Server B
  3. 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
  4. Client A sends the remaining 3 segments
  5. Again, Server B must send back an ACK to confirm it has received the other 3 segments

TCP Session Termination

  1. Client A sends segment to server B with the FIN flag to terminate the client-to-server session
  2. Server B sends ACK to client A
  3. Server B sends FIN to client A to terminate the server-to-client session
  4. Client A sends ACK to server B
  5. The session closes

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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?
  • UDP is used for streaming (we need data fast because it’s in real time)
  • TCP used for passwords

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

  1. Which of the following IP Addresses are possible? Explain (yes/no) for each answer choice.
    • 1.1.1.1.1 (Not possible because IP addresses have 4 numbers but this one has 5 numbers)
    • 23.23.23.23 (Possible because there are only 4 numbers and the numbers are in between 0-255)
    • 134.492.100.0 (Not possible because it contains the number 492, which is outside of the range 0-255)
    • 255.256.55.255 (Not possible because it contains the number 256 which is outside of the range 0-255)
    • 2.93.255.19 (Possible because there are 4 numbers and each number is within the limit of 0-255)
  2. 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.
    • Multicast
    • Unicast
    • Broadcast

This is an example of a broadcast. In a broadcast, the message is addressed to a special broadcast address, and every device on the network, regardless of its unique address, receives and processes the message.

Models

  1. 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:
    • ASCII (see above for information)
      • Application: ASCII is concerned with how data is presented and understood by humans, making it more related to the application layer where user interaction and resource sharing occur.
    • FTP (facilitates transfer of files over the internet)
      • Application: FTP is designed to facilitate the transfer of files over a network. It involves user authentication, file management, and directory listing, which are application-level functions.
    • TLS (see HTTPS section)
      • Application: TLS is used to secure communication between applications. It operates above the transport layer protocols (such as TCP) and below the application layer protocols (such as HTTP or SMTP). This positioning allows TLS to provide security services to the protocols at the application layer.
    • USB (permits data exchange between electronics)
      • Physical: USB permits data exchange at the physical level by providing a standard interface for connecting and transferring data between electronic devices.
  2. 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 belongs to the application layer. Telnet is a protocol used for remote terminal access. It allows a user on one computer to log into another computer on the same network or the internet and execute commands as if they were directly connected to the remote machine.
  • The application layer, layer 7, serves as a crucial interface between the network and end-user applications. Its primary function is to provide network services directly to applications, enabling seamless communication between software running on different devices. This layer defines communication protocols and standards specific to various applications, facilitating data exchange, format representation, and encryption if necessary.

DNS

  1. 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?
    • Bob needs to puchase the domain “best.com”. The subdomains would be “bob.is.the”.

HTTP and HTTPS

  1. What is a difference between HTTP and HTTPS?
    • What protocol does HTTPS use that HTTP doesn’t?
    • HTTP does not provide any encryption, while HTTPS adds a layer of ecurity using SSL/TLS encryption.
  2. Last trimester we sent HTTP requests for our passion projects
    • Did we use HTTP or HTTPS?
    • We used HTTP requests - What are the benefits and disadvantages of this?
    • HTTP is a simpler protocol compared to HTTPS, therefore data transfers faster and can be useful when encryption and security are not necessary (like our passion project). HTTP is also universally supported and very compatible. The disadvantages are that is lacks encryption and there is no data integrity, meaning the data could have been tampered with during transmission.

TCP and UDP

  1. 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?
    • He should use UDP because it has less delay as it doesn’t need to establish a connection and does not have error recovery mechanisms that may introduce delays to the stream. - What are some cons of this protocol? Give an example of a potential issue.
    • One con to using UDP is the potential packet loss that can happen. Since there is no error recovery in UDP, if a packet is lost during transmission it wont be retransmitted. This can result in video glitches.
  2. 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.
    • It is important to ensure that all packets arrive properly because many types of applications rely on accurate and complete data transmission. Applications that demand reliable data delivery, such as file transfers, email communication, and web browsing, rely on TCP to ensure that all data reaches the destination accurately and in the correct order. One example of error checking that TCP does is assigning sequence numbers to each TCP segment. The sender assigns sequence numbers to the segments to indicate the order in which they were sent. Then, the receiver sends acknowledgment numbers back to the sender to confirm the successful receipt of segments. If the sender does not receive an acknowledgment for a particular segment, it assumes that the segment was not received and retransmits it.
  3. 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?
    • In TCP, after the packets are sent to Server B, Server B will send an ACK Server A waits for this acknowledgment before sending the next packet. If an acknowledgment is not received within a certain timeout period, Server A assumes that the packet was lost or not delivered successfully, and it retransmits the packet.
    • In UDP, Server A does not wait for any acknowledgement that the packets were recieved. It will just continue sending packets and expect that Server B has recieved them. - What is another use of this?
    • Another use of the acknowledgment mechanism in TCP is to support flow control. Flow control helps prevent a fast sender (Server A) from overwhelming a slower receiver (Server B) by ensuring that the receiver can handle the incoming data at its own pace.