Network Protocols

Basic concepts

• TCP/IP model layers

  

  

  • Add header from the higher leyer to the lower layer

  

• Process of data transmission

  

  • From higher layer to lower laryer in sender, From lower layer to higher layer in receiver

  

• Client: sends/requests data to server
  • A single machine can be both client and server at the same time. eg. A single machine could acts as a aserver for end users and client for a database.

• Server: returns data/service to the client, listening for incoming network calls

• port: 16,000 ports in one machine eg HTTP 80, HTTPS 443 port#

• IP address: Address that each machine connected to the public Internet. a.b.c.d (four numbers are all (0, 255))
  • 127.0.0.1 is to localhost, 192.168.a.b is to private network, have 192.168 prefix, internal network.
• IP: Internet protocal, IP address. IP packet: stored in bytes

  • IP header:

    source IP address, destination address, total size of packet, internet IP version IPV4 or IPV6

    Payload: data to send(2^16 bytes) so we need multiple ip packets (TCP) for large files

• TCP: transmission control protocal. Send IP packet in order. Error free way, resend if incorrect. Build on top of IP.
  • Allow for ordered, reliable data delivery between machines over the public internet by connection.

  • TCP structure:

    IP header

    TCP header

    data

  • TCP connection, handshake, timed out, end the connection, sockets to applications
• HTTP: HeperText transfer protocol. request-response paradigm. More business logical than IP and TCP. Build on top of TCP.
  • http request: host, port, method(get, put, post, delete), path, headers, body, cookie
  • http responces: statusCode, headers, body
  • Difference between POST and PUT?

    

Try examples

Mock client and server

Send data to local machine port nc 127.0.0.1 8081 (terminal1) Listen data from local machihe port nc -l 8081 (terminal1) You can send data from the first terminal

Find IP address of a public url

find IP address in Mac dig google.com

Send/retrive data to servers

curl localhost:8080/world default http, get

What happened when you enter an url to your browser

Video reference

browser(client) -> DNS query(IP address) -> send HTTP request(IP packet) -> Google.com(server) -> reponse HTML/CSS to clients

1. Initial typing: auto complement, history and local cache
2. Url parsing: url or search words

3. Find protocol: HTTPS 443 (default) or HTTP 80

4. DNS lookup (domain name server): IP address, local cache or DNS over HTTPS
   • DNS is UDP server, send packet, send to router via to NAT gateway, get response from ISP(Internet Service Provider ) of IP address of google.com
5. TCP connection: 3 way handshake to build connection, go through many routers
   • Client Hello, server Hello, TLS protocol, Client key exchange, Server key exchange
6. GET request: Cookie together with the get request, send the header, response with the HTML web page body
   • http request: host, port, method(get, put, post, delete), path, headers, body, cookie
   • passowrd and username: token, store in cookie. Check whether is the correct person to log in.
   • http responces: statusCode, headers, body
7. HTML parsing: content-type html, image, html, js, css

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