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## **4 layers of the TCP/IP model**

The TCP/IP model consists of **four layers**, listed *from bottom to top*.

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### **1. Network Access Layer**

Combines OSI layers **1 and 2**.

Functions:

- transmitting frames over the physical medium
- working with MAC addresses
- Ethernet, Wi-Fi, PPP

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### **2. Internet Layer**

Equivalent to the **OSI network layer (L3)**.

Functions:

- IP addressing
- routing
- delivering packets between networks

Protocols:

- IPv4 / IPv6
- ICMP / ICMPv6
- ARP / NDP
- OSPF, BGP, RIP

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### **3. Transport Layer**

Equivalent to **OSI layer 4**.

Functions:

- segmentation
- delivery management
- TCP/UDP ports

Protocols:

- **TCP**
- **UDP**

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### **4. Application Layer**

Combines **OSI layers 5, 6, and 7**.

Functions:

- network services for applications
- working with upper-layer protocols

Protocols:

- HTTP/HTTPS
- DNS
- FTP/SFTP
- SMTP/IMAP/POP3
- DHCP
- SSH
- SNMP

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## **Short answer for an interview**

> **The 4 layers of TCP/IP: Network Access, Internet, Transport, Application.**

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## **Cheat sheet (5 seconds)**

**TCP/IP:**

1. **Network Access**
2. **Internet**
3. **Transport**
4. **Application**

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