## DNS (Domain Name System)

DNS turns human names (`google.com`) into computer IPs (`142.250.72.14`).

### The DNS Hierarchy
1.  **Root Hints (.)**: The 13 root servers worldwide. They know who handles `.com`, `.org`, etc.
2.  **TLD (Top Level Domain)**: The `.com` servers. They know who handles `google.com`.
3.  **Authoritative Name Server**: Google's actual server. It knows the IP.

### The Resolution Process
You type `google.com`.
1.  **PC**: Checks local cache / HOSTS file.
2.  **Recursive Resolver (ISP/8.8.8.8)**: "I don't know. I'll ask Root."
3.  **Root**: "I don't know, ask .COM server."
4.  **.COM**: "I don't know, ask ns1.google.com."
5.  **ns1.google.com**: "I know! It is 1.2.3.4."
6.  **Resolver**: Caches it and gives it to PC.

### Record Types
*   **A**: IPv4.
*   **AAAA**: IPv6.
*   **MX**: Mail Server.
*   **CNAME**: Alias.
*   **PTR**: Reverse DNS (IP -> Name). Used for email filtering.
*   **TXT**: Arbitrary text (SPF/DMARC).