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Networking

From typing an address to receiving the response: DNS, TCP, HTTP, TLS, and the machines in between.

The big picture

• From URL to response — What happens when you type a URL in the address bar and press Enter
• Layers and encapsulation — You send 1500 bytes, so why do 1616 bytes cross the wire?

Addresses and names

• URL structure — After I added the search term "A&B" to the URL, the server received only "A"
• DNS — Who knows the IP address of a domain name, and when does a change show up?
• IP addresses and subnets — Are two IP addresses with the same first three numbers on the same network?
• Switches and routers — If the destination IP is the server, why is the frame sent to the router's MAC address?

Transport layer

• Sockets and ports — Of the several programs on one computer, which one receives this data?
• TCP connections and retransmission — When a packet is lost, who notices and sends it again?
• TCP and UDP — If you send data in three pieces, does it arrive in three pieces?
• Flow control and congestion control — How does TCP decide how much to send at a time?

HTTP

• HTTP messages and status codes — This is what a request and a response look like as text
• HTTP/1.1, 2, 3 — What differs between the versions when you fetch 30 files
• Cookies — Showing a name tag, every time, to a server that cannot remember you
• HTTP caching and ETag — Do we have to fetch the same file again?
• Retries and idempotency — No response came back, so the request was sent again
• Redirection — When a server says "go to another address", how does the next request go out?
• Content negotiation and compression — Why do different people get different responses from the same address?
• CORS — Why a request works in Postman but is blocked only in the browser
• Polling, SSE, and WebSocket — Four ways to tell the browser what happened on the server

Secure connections

• TLS handshake — What happens before the https padlock locks

In front of the web server

• Load balancers and scale out — How far does adding servers get you?
• Proxies and reverse proxies — How does a server behind a proxy know who sent the request?
• CDN — The origin was changed, so why do users still get the old file?