CS208 Introduction to Computer Systems
Friday, 14 November 2025

+ Exam, closed-book, Monday Nov 17
- Questions?
    - LEA (see slides)
    - Loops

+ Network starter vocabulary
- IP address: a number that gives you the
    "address" of a computer within a network
- server
    - a piece of software that listens for requests and
        responds to those requests
    - a computer that gives files to clients (one kind of server)
        - a computer that runs server software
- server examples
    web server (nginx, IIS, Apache,...)
    ssh server (OpenSSH = sshd, ...)
    email server
    date server (provides current date and time)
    ...
- port
    ...
- client
    - a piece of software that makes requests of one or more servers
- client examples
    - Chrome, Firefox, Safari, Edge,...
    - ssh
    - ...
- protocol
    - ...

+ Setup
- macOS
    - nc installed by default (check with "which nc")
    - get your IP address on the Carleton network
        ifconfig | grep inet
        [look for one that starts with 10.13X...]
- Windows
    - get nc (do you trust me?)
        https://cs.carleton.edu/faculty/jondich/local/nc.exe
    - get your IP address
        ipconfig

+ Questions for the experiments
- What's the server?
- What's the client?
- What's the protocol?

+ Network experiment 1
- two laptops

- IP addresses

- laptop 1
    cd to a directory containing non-private files
    python3 -m http.server 5555

- laptop 2
    curl -v http://LAPTOP1_IP_ADDR:5555/

+ Network experiment 2
- laptop 1
    cd to a directory containing non-private files
    python3 -m http.server 5555

- laptop 2 (macOS today, since nc is installed by default)
    nc LAPTOP1_IP_ADDR:5555
    GET / HTTP/1.1
    [blank line]   

+ Network experiment 3
- laptop1
    nc -l 5555   [macOS]
    nc -l -p 5555  [other]

- laptop2
    nc LAPTOP1_IP_ADDR 5555
    [type stuff]

+ Under the hood
- TCP connections
- sockets