The Cisco TCP/IP model has 5 layers – the Network Access layer is split into Data Link and Physical.
| Layer | Name | Primary function | Scope | Typical protocols | Data unit |
|---|---|---|---|---|---|
| 5 | Application | Network services for applications | Application-to-application | HTTP, HTTPS, FTP, SMTP, DNS, DHCP, SNMP, SSH, NTP | Messages |
| 4 | Transport | End-to-end transport, ports, reliability | End-to-end / host-to-host | TCP, UDP, SCTP | Segments / datagrams |
| 3 | Internet | Logical addressing and routing | End-to-end (via routers) | IP, ICMP, IPsec | Packets |
| 2 | Data Link | Framing, MAC addressing, local delivery | Hop-by-hop / node-to-node | Ethernet, Wi-Fi, ARP, PPP | Frames |
| 1 | Physical | Physical transmission of bits | Bit-for-bit | Copper, fiber, radio | Bits |
Classic TCP/IP vs Cisco TCP/IP
| Classic TCP/IP (4 layers) | Cisco TCP/IP (5 layers) |
|---|---|
| Application | Application |
| Transport | Transport |
| Internet | Internet |
| Network Access | Data Link + Physical |
Exam note (very important) ⚠️
- Cisco accepts both models
- Cisco material most often uses the 5-layer model
- OSI is used for troubleshooting and concept understanding