Client Server Model

Clients

• A client is something that queries servers.
• e.g. A browser, or mobile device

Servers

• A server is something that responds to requests.
• e.g. a Website backend

Networking

Making a GET Request

• When a browser looks up a website, it does a DNS lookup of the URL to find its IP Address
• a DNS query goes to a set of servers, and the server returns the IP address.
• an IP address is a unique id for public computers.
• an IP address is like a mailbox for a computer.
• dig domain makes a DNS query.

Server Response

• With the IP address, the HTTP server knows where to send its request.
• The client can then send messages to it, and the server can respond to those messages with its own messages.
• HTTP is over TCP/IP, which is normally on port 80.
• HTTPS is over TCP/IP with TLS, which is normally on port 443.

Exercise

• Use nc -l 8081
  • This listens on port 8081
• Use nc 127.0.0.1 8081 to connect to port 8001.
  • This connects to the client on port 8081.
    • Send messages to see them on both terminals.

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