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

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? Would fall under presentation, because it’s a representatino of data just like how you can represent data in different ways.
  • Another example is AFP, which is actually it’s own network protocol that can communicate sepcifically only to macs!!!! In a way it acts as an example of FTP similar to

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!
  • I did this

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
  • youtube.com, github.com, discord.com, google.com
  • What’s a subdomain of your passion project backend from last time?
  • napoleon-bonaparte-official
  • What’s the domain of your current binary CPT project?
  • github, the .io is technichally just an extension

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!
    • Streaming when you need it really fast and you don’t need the data to be super reliable
  • When might we use TCP?
    • emailing because reliable information is crucial for emails.

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 - no not possible becuase there shouldn’t be more then four digits in a IPv4 address or IPv6 addresses.
    • 23.23.23.23 - yeah i mean it’s four octets and the numbers range from 0 - 255
    • 134.492.100.0 - no the second octet contains a number greater then 255 so no
    • 255.256.55.255 - the second octet also contains a number greater then 255 so no
    • 2.93.255.19 - yes there are four octets and the numbers range from 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 - It’s not multicast, because while multicast does send it all over the internet
    • Unicast - This literally only sends it to one device on the internet
    • Broadcast - Does exactly what we want, sends to all devices on the network

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) - ASCII is on the presentation layer and they’re on that layer because it’s a different method of presenting data
    • FTP (facilitates transfer of files over the internet) - Application layer, it handles end to end communications just like any other application would do and thus it’s in this application layer
    • TLS (see HTTPS section) - I’d say goes onto the presentation format, becuase the encryption and presentation layer actually handles encryption
    • USB (permits data exchange between electronics) - Physical for sure, because it’s physically on the device
  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?
    • Application it’s handling end to end requests as an application

      DNS

  3. 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? The domain he should the best.com because i mean the rest are just like subdomains, the sub domain 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? HTTPS uses the TLS layer while HTTP does not
  2. Last trimester we sent HTTP requests for our passion projects
    • Did we use HTTP or HTTPS? we used HTTPs with the certbot
    • What are the benefits and disadvantages of this? Provides an extra layer of security and encryption

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? UDP, you don’t need super reliable information for example if small information is lost while streaming it’s not nearly as important as the speed and keeping the stream real time
    • What are some cons of this protocol? Give an example of a potential issue. Some cons of this protocol is that it isn’t super reliable and thus he might lose a little bit of the strileaming information and there might be times where it might get a bit blurry or some buffering issues.
  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.
    • An example of how TCP has error checking is acknowledgement (ACK) where it sends data and acknowledges a confirmatino, otherwise if there’s an error it will retransmit. It’s important to have all packets arrive because then you can get the reliable information that you need when transmitting important information over. In other words the TCP handshake.
  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?
    • The three-way handshake ensures that both Server A and Server B are aware of the established connection.
    • Once the connection is established, data transmission can occur. Server A sends data, and Server B acknowledges the receipt of that data.
    • Server B ensures it has received the data correctly by sending ACKs back to Server A.
    • What is another use of this?
    • Another use of ensuring packet receipt in TCP is maintaining a reliable and ordered data transfer. By confirming receipt and requesting retransmission if necessary, TCP ensures that data is received correctly and in the correct sequence, crucial for applications like file transfers and web browsing where data integrity is paramount.