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--- networking:dns [2026/07/22 19:39] – [Telenegar DNS Check] admin
+++ networking:dns [2026/07/22 20:46] (current) – removed - external edit (Unknown date) 127.0.0.1
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-====== DNS Explained ======
-The **Domain Name System (DNS)** is often described as the "phonebook of the Internet." It translates human-readable domain names (such as `example.com`) into IP addresses (such as `93.184.216.34`) that computers use to communicate.
-Without DNS, users would have to remember the IP address of every website they visit.
------
-===== How DNS Works =====
-When you enter a domain name into your browser, the following steps occur:
-  - **Resolver** (usually your ISP's DNS server or a public resolver such as Google DNS `8.8.8.8` or Cloudflare DNS `1.1.1.1`) receives the query.
-  - The resolver checks whether it already has the answer cached.
-  - If not cached, the resolver queries a **Root DNS Server**.
-  - The root server directs the resolver to the appropriate **Top-Level Domain (TLD) Server** (such as `.com`, `.org`, or `.ir`).
-  - The TLD server tells the resolver which **Authoritative DNS Server** is responsible for the domain.
-  - The authoritative server returns the requested DNS record (A, AAAA, MX, TXT, etc.).
-  - The resolver caches the answer according to its **TTL (Time To Live)** and returns it to your browser.
-<code>
-Browser
-   │
-   ▼
-Recursive Resolver
-   │
-   ▼
-Root Server
-   │
-   ▼
-TLD Server
-   │
-   ▼
-Authoritative DNS Server
-   │
-   ▼
-DNS Record
-</code>
------
-===== Common DNS Record Types =====
-^ Record ^ Purpose ^ Example ^
-| **A** | Maps a hostname to an IPv4 address | `example.com → 93.184.216.34` |
-| **AAAA** | Maps a hostname to an IPv6 address | `example.com → 2606:2800:220:1:248:1893:25c8:1946` |
-| **CNAME** | Alias for another hostname | `www.example.com → example.com` |
-| **MX** | Mail server for a domain | `10 mail.example.com` |
-| **TXT** | Text information (SPF, DKIM, DMARC, ownership verification, etc.) | `v=spf1 include:_spf.example.com ~all` |
-| **NS** | Authoritative name servers for a zone | `ns1.example.com` |
-| **SOA** | Zone configuration and serial number | `ns1.example.com admin.example.com 2026072001` |
-| **PTR** | Reverse DNS (IP → hostname) | `93.184.216.34 → example.com` |
-| **CAA** | Specifies which Certificate Authorities may issue TLS certificates | `0 issue "letsencrypt.org"` |
------
-===== Recursive Resolver vs Authoritative Server =====
-It is important to distinguish between these two server types.
-^ Recursive Resolver ^ Authoritative Server ^
-| Receives queries from users | Stores the official DNS records |
-| Performs recursive lookups | Answers only for its own domains |
-| Caches results | Does not perform recursion |
-| Usually operated by ISPs or public DNS providers | Usually operated by the domain owner or DNS provider |
------
-===== What is an Authoritative DNS Server? =====
-An **authoritative DNS server** stores the official DNS records for a domain.
-Example:
-<code>
-example.com
-    │
-    └── ns1.example.com
-            ├── A      → 93.184.216.34
-            ├── AAAA   → 2606:...
-            ├── MX     → mail.example.com
-            ├── TXT    → v=spf1 include:_spf.example.com ~all
-            └── CAA    → letsencrypt.org
-</code>
-Whenever DNS information changes, these servers are the source of truth.
------
-===== What is TTL? =====
-**TTL (Time To Live)** specifies how long a DNS record may be cached before it must be queried again.
-Example:
-| TTL | Meaning |
-| 300 | Cache for 5 minutes |
-| 3600 | Cache for 1 hour |
-| 86400 | Cache for 24 hours |
-Short TTL values allow DNS changes to propagate more quickly but increase the number of DNS queries.
------
-===== Why do different DNS servers sometimes return different answers? =====
-DNS responses may vary because:
-  * Different resolvers may still have cached records.
-  * CDN providers return different IP addresses based on the user's geographic location.
-  * DNS propagation may still be in progress after a recent change.
-  * Some providers implement GeoDNS or Anycast routing.
-This is why querying multiple DNS servers is useful when troubleshooting DNS issues.
------
-===== DNS Propagation =====
-After changing a DNS record, not all users will see the change immediately.
-Propagation time depends on:
-  * The TTL of the previous record.
-  * Resolver cache expiration.
-  * ISP caching policies.
-Although changes are published immediately on the authoritative server, recursive resolvers around the world may continue serving cached data until the TTL expires.
------
-===== Telenegar DNS Check =====
-**Telenegar DNS Check** queries DNS records from multiple DNS providers and geographic locations, allowing you to:
-  * Compare responses from different DNS servers.
-  * Detect DNS propagation issues.
-  * Verify GeoDNS and CDN behavior.
-  * Query A, AAAA, MX, TXT, NS, SOA, PTR, CNAME, and other DNS record types.
-Use our [[https://telenegar.ir/dnscheck/|DNS Check]] tool to investigate DNS resolution from multiple locations.
------
-===== See Also =====
-  * [[networking:dns-propagation|DNS Propagation Explained]]
-  * [[networking:cdn|CDN and GeoDNS Explained]]
-  * [[networking:dnssec|DNSSEC Explained]]
-  * [[https://telenegar.ir/dnscheck/|Telenegar DNS Check]]
------
-{{tag>dns networking dnssec authoritative resolver propagation ttl}}