Application protocols

Vocabulario

English	Significado
DNS/ˌdiː en ˈes/	DNS
HTTP/ˌeɪtʃ tiː tiː ˈpiː/	A request-response grammar: request line, headers, blank line, body — and the status codes class is the promise: 2xx success, 3xx redirect, 4xx client error, 5xx server error.

English

Resolve the name

DNS turns a name into an address by hierarchical delegation: the root knows the TLD servers, .com knows the registrars, the authoritative server knows the host. Each answer is a referral downward, and caching skips the walk for the answer's TTL.
HTTP is a request-response grammar: request line, headers, blank line, body — and the status codes class is the promise: 2xx success, 3xx redirect, 4xx client error, 5xx server error.

{exercise:uni-cs0905-dns}

Práctica

DNS delegation means the root answers with —

Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy

English

GET /index.html HTTP/1.1 with a Host header; the server answers 200 OK, headers (Content-Type, Content-Length: 128), blank line, exactly 128 body bytes.
The blank line is load-bearing: the parser waits for exactly those two newlines. Content-Length counts body bytes only — headers are counted by the blank line's position.

{exercise:uni-cs0905-bytes}

Práctica

The header block ends at —

Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy

English

200 (here is the body), 301 (it moved — Location says where), 404 (you asked wrong), 500 (I broke). A crawler treats 301 as a pointer, 404 as a dead end, 500 as retry-later.
One global name table would be one global outage: delegation splits the failure domain as well as the data.

{exercise:uni-cs0905-codes}

Práctica

A 301 response tells the client —

Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy