Yaya DNS resolution ke aiki?

Question

IT Interview Practice · Accepted Answer

**DNS** (Domain Name System) shine littafin waya na intanet: yana fassara sunan da mutum zai iya karantawa kamar `example.com` zuwa adireshin IP kamar `93.184.216.34`. Resolution bincike ne na matsayi, galibi ana yin sa maka ta **recursive resolver** (na ISP ɗinka ko na jama'a kamar 8.8.8.8) wanda ke tafiya cikin bishiyar sunayen server na **authoritative** a madadinka:

```text
Browser ──▶ Recursive Resolver ──▶ Root (.)          "ask .com's servers"
                     │        ◀──
                     ├────────▶ TLD (.com)            "ask example.com's servers"
                     │        ◀──
                     └────────▶ Authoritative         "example.com = 93.184.216.34"
                                (example.com)   ◀──
Browser  ◀── 93.184.216.34
```

Resolver yana tambayar servers na **root** (waɗanda suka san servers na TLD), sannan servers na **TLD** don `.com` (waɗanda suka san wanda ke authoritative ga `example.com`), sannan server na **authoritative** (wanda ke riƙe ainihin record). Don guje wa maimaita wannan kowane lokaci, ana **cache** sakamakon a kowane mataki — browser, OS, da resolver — kowanne yana girmama **TTL** (time-to-live) na record. Cache mai zafi yana resolve cikin microseconds; bincike mai sanyi na iya kashe zagaye da yawa.

Nau'ikan **record** na kowa: `A` (name → IPv4), `AAAA` (name → IPv6), `CNAME` (alias zuwa wani suna), `MX` (mail servers), `TXT` (rubutu na kowane iri, ana amfani da shi ga SPF/tabbatarwa), da `NS` (yana wakilta zone). Za ka iya duba resolution kai tsaye:

```bash
dig example.com A       # yana nuna record na A da wanne server ya amsa
```

## Me ya sa yake da muhimmanci

DNS yana zaune a kan hanya mai muhimmanci na *kowane* request da ke farawa daga suna, don haka resolver mai jinkiri ko wanda aka saita ba daidai ba yana ƙara latency ga komai. Masu hira suna son wannan tambaya saboda tana bayyana ko kana fahimtar **matsayi da caching** — ra'ayoyi biyu da ke bari tsari na duniya, mai rarrabuwa amsa biliyoyin tambayoyi da sauri. Yana kuma zama tushen sau da yawa na ainihin abubuwan da suka faru na production ("koyaushe DNS ne"): records da suka ƙare, TTL marasa daidai, ko jinkirin yaɗawa bayan canji, don haka sanin yadda caching da TTL ke aiki mai amfani ne kai tsaye.

Me ya sa yake da muhimmanci

Tambayoyi masu alaƙa