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
  • I did this, but I’m not typing my ip address here LOL.

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 (ex: USB) 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? Layer 6 (presentation), since it translates binary to human text.
  • Give another example of a protocol from that layer. TLS is another layer 6 protocol.

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 got 142.250.217.142 instead, but the link still directs to google!

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?
  • Website: IP. Dynamic Periodic Table: 209.18.47.61. YouTube: 209.18.47.61. Discord: 209.18.47.61. Gmail: 209.18.47.61.

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 (from one place to another). 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 since need to send information fast and doesn’t have to be 100% accurate.
  • When might we use TCP? Databases, banking, etc., as accuracy is very important.

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, there are 5 numbers rather than 4
    • 23.23.23.23 - Yes, all 4 numbers are all within 0 and 255
    • 134.492.100.0 - No, 492 is not within 0 and 255
    • 255.256.55.255 - No, 256 is not within 0 and 255
    • 2.93.255.19 - Yes, all 4 numbers are within 0 and 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, because it is sent to all computers on the network, not a specific or group of 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) - Layer 6, it translates binary to human text
    • FTP (facilitates transfer of files over the internet) - Layer 7, because FTP essentially packages the data and sends it out
    • TLS (see HTTPS section) - Layer 6, it encrypts data which appears to be part of translating data between computer data and human text
    • USB (permits data exchange between electronics) - Layer 1, a physical object that can move data from computer to computer
    • Also, ASCII is definitely 6, TLS is definitely 7, and USB is definitely 1. Are there some that overlap layers and result in 3 of the 4 having the same layer?
  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 would fall on Layer 7 since it connects computers and allows interaction. Layer 7 is the application layer and is responsible for user interaction such as resource sharing.

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?
    • He should buy the domain “best.com” and the subdomain should be “bob.is.the”, since the domain is the last text after the 2nd-to-last “.” and then .(smth) (like .com), and the subdomain is everything before that.

HTTP and HTTPS

  1. What is a difference between HTTP and HTTPS? The difference between HTTP and HTTPS is that while both trasmit data over the internet, HTTPS adds security using SSL/TLS encryption.
    • What protocol does HTTPS use that HTTP doesn’t? SSL/TLS, see above.
  2. Last trimester we sent HTTP requests for our passion projects
    • Did we use HTTP or HTTPS? HTTP, says it in the question.
    • What are the benefits and disadvantages of this? Since HTTP doesn’t require encryption and decryption, HTTP is faster. On the other hand, the data is less secure and vulnerable to attacks.

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? If Bob needs the stream to be real time, then he should use UDP because it is faster than TCP. UDP doesn’t have the ACK messages that TCP uses, so the movement of packets is quicker.
    • What are some cons of this protocol? Give an example of a potential issue. The con of using UDP over TCP in this case is the cost of more unreliable data as no ACK messages are used so the connection and transmission of data isn’t confirmed and isn’t the most reliable. However, this doesn’t matter that much in video streaming since showing the video on time is more important than a slight error in the image (that probably won’t be noticed because only a small number of packets are wrong).
  2. TCP has error checking, which ensures that all packets arrive properly. Why is this important? Error checking to ensure that the packets arrive properly is very important because the TCP handshake has a specific sequence for how to inititate it and the right packets need to arrive at the right time in the right order, so the right data is sent properly.
    • Give an example of how TCP ensures that there are no errors. Before any data is sent, both computers must acknowledge each other (computer 1 send SYN to computer 2, computer 2 sends a SYN-ACK to computer 1, and computer 1 sends ACK to computer 2, and all of these must be properly sent and received) to ensure that the connection is properly made. Then data is actually sent, and then another process with mutual acknowledgement as well to terminate the connection occurs as well.
  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? For TCP, the data sent is split into 6 parts, and initially only the first 3 parts are sent. Server B must send back an ACK before the second 3 parts are sent, and then Server B sends another ACK at the end. For UDP, there are no ACK packets sent or acknowledged and Server A just sends all the packets.
    • What is another use of this? ACK in TCP can also adapt to network conditions and alter the rate it sends packets to help alleviate congestion or packet loss.