# Network

##

| Layer Number | ISO OSI Model      | TCP/IP Model (RFC 1122) | Protocols                                        | Main Function                                         |
| ------------ | ------------------ | ----------------------- | ------------------------------------------------ | ----------------------------------------------------- |
| 7            | Application Layer  | Application Layer       | HTTP, HTTPS, FTP, POP3, SMTP, IMAP, Telnet, SSH, | Providing services and interfaces to applications     |
| 6            | Presentation Layer |                         | Unicode, MIME, JPEG, PNG, MPEG                   | Data encoding, encryption, and compression            |
| 5            | Session Layer      |                         | NFS, RPC                                         | Establishing, maintaining, and synchronising sessions |
| 4            | Transport Layer    | Transport Layer         | TCP, UDP                                         | End-to-end communication and data segmentation        |
| 3            | Network Layer      | Internet Layer          | IP, ICMP, IPSec                                  | Logical addressing and routing between networks       |
| 2            | Data Link Layer    | Link Layer              | Ethernet 802.3, WiFi 802.11                      | Reliable data transfer between adjacent nodes         |
| 1            | Physical Layer     |                         | Electrical, optical, and wireless signals        | Physical data transmission media                      |

## DNS record type

| **DNS Record**   | **Description**                                                                        |
| ---------------- | -------------------------------------------------------------------------------------- |
| **A Record**     | Holds the IPv4 address of a domain.                                                    |
| **AAAA Record**  | Contains the IPv6 address of a domain.                                                 |
| **CNAME Record** | Forwards one domain or subdomain to another domain but does not provide an IP address. |
| **MX Record**    | Directs email to an email server.                                                      |
| **TXT Record**   | Allows admins to store text notes in the record, often used for email security.        |
| **NS Record**    | Stores the name server for a DNS entry.                                                |
| **SOA Record**   | Stores administrative information about a domain.                                      |
| **SRV Record**   | Specifies a port for specific services.                                                |
| **PTR Record**   | Provides a domain name in reverse DNS lookups.                                         |
