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Reference

Lookup pages for when you know the topic and need the number. Ports and protocol numbers, header bit diagrams, latency and capacity figures, decision matrices for the classic tradeoffs, a glossary, and a map from error messages to causes. Every figure is sourced or derived on its page, and each entry links to the topic page that explains it. The last page collects every interview question in the course.

What you will be able to answer​

  • Which port and transport does a service use, which IP protocol number is TCP, UDP or ICMP, and what is the ephemeral port range on Linux, macOS and Windows?
  • Where does each field sit in the Ethernet, IPv4, IPv6, TCP, UDP, DNS, TLS, HTTP/2 and QUIC headers, and how wide is it?
  • What is the latency floor for a given distance, how many round trips does a cold HTTPS request cost on TLS 1.2, TLS 1.3 and QUIC, and how do you size a link or a connection count on the back of an envelope?
  • Which option wins for TCP vs UDP vs QUIC, REST vs gRPC, L4 vs L7, security group vs NACL, or peering vs transit gateway, and what is the deciding factor?
  • What does a term mean, what does it expand to, and which terms mean two different things?
  • What happened on the wire when you see ECONNREFUSED, ETIMEDOUT, ECONNRESET, EADDRINUSE, NXDOMAIN, 502 or 504, and what is the first command to run?
  • Which interview questions has the course covered, by module and level?
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