Foundations / Beginner / 6 min
Everything before the first byte
DNS, TCP, TLS and HTTP packet by packet. Compare HTTP/1.1, HTTP/2 and HTTP/3 across the world.
Start the simulation → Change the load, break a part, watch what happens. Free, no sign-up.
In short
- What it is
- Before any data moves, the browser does a DNS lookup, a TCP handshake and a TLS handshake, each costing round trips.
- Why it matters
- Round trips are limited by distance and the speed of light, so a far server is slow no matter how fast it is.
- The trade-off
- CDNs and edge servers cut the distance but add cost and make fresh data harder to serve; keep-alive and HTTP/2 reuse connections.
- Say it in an interview
- "Latency is mostly round trips times distance, so I would serve static content from a CDN close to the user."
Check yourself
Which protocol combination needs the fewest round trips before the first request can be sent on a new connection?
Answer: HTTP/3 over QUIC. QUIC combines the transport and TLS 1.3 handshakes into one round trip, and runs over UDP so there is no separate TCP handshake.
Why does a keep-alive connection make the second request much faster?
Answer: It skips the TCP and TLS handshakes. The connection is already open and encrypted, so only the request and response round trip remains.
A full DNS lookup walks which chain?
Answer: Resolver → root → TLD → authoritative name server. The resolver asks a root server for the TLD servers, the TLD for the domain’s name servers, then the authoritative server for the address.