Differences

This shows you the differences between two versions of the page.

--- networking:dns [2026/07/21 15:48] – external edit 127.0.0.1
+++ networking:dns [2026/07/21 18:18] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 ====== DNS Explained ======
-The Domain Name System (DNS) is like the phonebook of the internet. It translates human-readable domain names (like `example.com`) into IP addresses (like `93.184.216.34`) that computers use to communicate.
+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.
 -----
@@ Line 7: / Line 9: @@
 ===== How DNS Works =====
-When you type a domain name in your browser, a series of queries happens:
+When you enter a domain name into your browser, the following steps occur:
-. **Resolver** (your ISP or public DNS like 8.8.8.8) receives the query
+  - **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.
-. **Root Server** tells which TLD server to ask
+  - The resolver checks whether it already has the answer cached.
-. **TLD Server** (.com, .org, .ir) tells which authoritative server to ask
+  - If not cached, the resolver queries a **Root DNS Server**.
-. **Authoritative Server** provides the final answer
+  - 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>
 -----
-===== DNS Record Types =====
+===== Common DNS Record Types =====
-^ Record Type ^ Purpose ^ Example ^
+^ Record ^ Purpose ^ Example ^
-| **A** | Maps domain to IPv4 address | `example.com → 93.184.216.34` |
+| **A** | Maps a hostname to an IPv4 address | `example.com → 93.184.216.34` |
-| **AAAA** | Maps domain to IPv6 address | `example.com → 2606:2800:220:1:248:1893:25c8:1946` |
+| **AAAA** | Maps a hostname to an IPv6 address | `example.com → 2606:2800:220:1:248:1893:25c8:1946` |
-| **CNAME** | Alias (canonical name) | `www.example.com → example.com` |
+| **CNAME** | Alias for another hostname | `www.example.com → example.com` |
-| **MX** | Mail exchange server | `mail.example.com` |
+| **MX** | Mail server for a domain | `10 mail.example.com` |
-| **TXT** | Text records (SPF, DKIM, etc.) | `v=spf1 include:_spf.example.com ~all` |
+| **TXT** | Text information (SPF, DKIM, DMARC, ownership verification, etc.) | `v=spf1 include:_spf.example.com ~all` |
-| **NS** | Name server | `ns1.example.com` |
+| **NS** | Authoritative name servers for a zone | `ns1.example.com` |
-| **SOA** | Start of authority (zone info) | `ns1.example.com admin.example.com 2026072001` |
+| **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"` |
 -----
-===== What is an Authoritative Server? =====
+===== Recursive Resolver vs Authoritative Server =====
-An **authoritative DNS server** is the final authority for a domain's DNS records. It holds the "official" records that are published in the DNS zone file.
+It is important to distinguish between these two server types.
-**Example:**
+^ 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 |
-| Domain | Authoritative Server | Records |
+-----
-|--------|---------------------|---------|
-| `example.com` | `ns1.example.com` | A → `93.184.216.34` |
+===== What is an Authoritative DNS Server? =====
-| | | MX → `mail.example.com` |
-| | | TXT → `v=spf1 include:_spf.example.com ~all` |
+An **authoritative DNS server** stores the official DNS records for a domain.
-Or visually:
+Example:
 <code>
 example.com
-  └── authoritative: ns1.example.com
+    │
-        ├── A     → 93.184.216.34
+    └── ns1.example.com
-        ├── MX    → mail.example.com
+            ├── A      → 93.184.216.34
-        └── TXT   → v=spf1 include:_spf.example.com ~all
+            ├── 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.
 -----
@@ Line 55: / Line 132: @@
 ===== Telenegar DNS Check =====
-Use our [[https://telenegar.ir/dnscheck/|DNS Check tool]] to query DNS records from global probes.
+**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.
 -----
-{{tag>dns networking dnssec}}
+{{tag>dns networking dnssec authoritative resolver propagation ttl}}