Networking Basics

• Every machine that needs to communicate over the internet, needs a public address (IP address - Internet Protocol Address), which allows us to specify where we want our msgs / data to go
  • IPv4 Address is a 32 bit integer → 4 billion unique IP addresses
  • IPv6 → 128 bits → Will probably never reach the limit
• For two machines to communicate, we need each ones unique identifier (IP address), and it’s like sending mail in real life (to.. from… address.., etc)
  • Internet Protocol → Rules for communicating between machines online
  • IP Packet → Has the data that is being sent, and the header contains the metadata (to, from, where, etc)
• The mechanism / service which allows communication to be structured, ordered, is done thru TCP (Transmission Control Protocol)
  • TCP breaks it down into more TCP header, which contains the information which allows it to re-assemble all of the data once reached destination
• The actual data which is inside of the packets, is called the application data
  • When we send HTTP requests, this is where the data is stored, and what we actually work with as a dev
• There are so many protocols going on (IP, HTTP, TCP), is because these are handled by different parts of the networking layers.

Routers and Misc

• Each of our device does not need to have a public IP address, but our router does
• This is b/c router can manage the traffic / DNS query on behalf of our devices
• Static IP address → IP addresses that do not change (i.e. think of printers in office, or fax machines, etc)
• Dynamic IP addresses → Dynamic DNS, we usually have clients as dynamic IP addresses as they’re always connecting / leaving
• Ports → Channel of communication between machines (besides networks); a 2^16 value → Approximately about 6500 ports available / machine
  • Can’t have multiple applications / pages running on same port
  • i.e. https is reserved for port 443, and http is reserved for port 80
  • local host is IP address 127.0.0.1, etc

TCP And UDP

• TCP establishes a connection between the two machines, which can now send data both ways → To do this, it does a 3-way connection (Send a msg to the server, server sends a response back, and then we send another msg from client to the server acknowledging it)
• TCP is reliable, but it’s slower because of the 3way handshake
• Exclusive pros:
  • Reliability → Re-transmission of lost packets (if a specific packet wasn’t received, it’ll ONLY resend that ONE lost / corrupt packet.
  • Keeping track of the order so we can re-assemble
• Examples which use TCP: HTTP (Web), Secure Mail Transfer Protocol (Emails), WS, etc
• UDP does not set up a handshake!
  • Not reliable → If a certain packet doesn’t arrive, its lost forever!
  • Data might arrive out of order too! → UDP does not correct them
  • However, UDP is ALOT faster than TCP
• UDP is used in streaming data in real time (Live streaming a video, or a call, playing online games, DNS, etc)
  • This means that its ok even if it lags a bit, or if a frame is glitched/out of order
  • No need to re-send those frames as we’re watching this live

DNS