CS208 Introduction to Computer Systems
Wednesday, 4 March 2026

+ Comps gala
- Tomorrow, 3:30-6:15
- Link to schedule in Slack

+ Questions on exam prep or whatever?

+ Networking assignment
- Story of "nc 129.6.15.28 13"
    - nc is program, and we launch it ("netcat", "ncat",...)
    - nc sends a request for a TCP connection to 129.6.15.28 at port 13
    - server at 129.6.15.28 port 13 agrees to the connection
        ---- TCP connection established ----
    - the client & server do the protocol
        (where is that written down? In "RFC 867")
        - for daytime, this is "server sends date/time and hangs up the phone"

- some notes
    - notion of a protocol
    - RFC's
    - looking at the HTTP stuff
    - one HTTP exercise I didn't include: "python3 -m http.server 8000"

+ Routing algorithms
- what is routing for?
    - the routing decision
    - routing tables
    - "network layer" or "IP layer" (and network layering in general)
    - macos: "netstat -rn -f inet"
      windows: same netstat command, or "route print -4"
      linux: "ip route"

- static routing
    preset routing decisions
- flooding (!)
    hand the packet to all immediate neighbors
- link-state routing
    - network graph & Dijkstra's algorithm
    - but what happens when the graph changes?

- why they had to reboot the internet on October 27, 1980
    (ok, looks like they just patched every machine without rebooting, but still)
    (RFC 789)