What are the four layers of the TCP/IP model, and which protocols belong to each?
Application (HTTP, DNS, SMTP, SSH), Transport (TCP, UDP), Internet (IP, ICMP), and Link (Ethernet, Wi-Fi, ARP). It merges OSI's top three layers into one and its bottom two into one.
Explain it simply
The TCP/IP model is what the internet actually runs. It is OSI squeezed down to four jobs: talk to the app, deliver between processes, route between networks, and move bits across one link.
Example
TCP/IP layer OSI layers Examples
Application 7, 6, 5 HTTP, HTTPS, DNS, SMTP, SSH, DHCP
Transport 4 TCP, UDP
Internet 3 IP, ICMP
Link 2, 1 Ethernet, Wi-Fi, ARPFollow one UPI app request: the app speaks HTTPS (application), TCP gives it a reliable connection to the bank's server on port 443 (transport), IP addresses the packets and routers forward them (internet), and your phone's Wi-Fi or mobile radio carries each hop (link).
ARP sits awkwardly between link and internet. Textbooks differ on where to place it, so just say it works on the local link.
What to say in the interview
"TCP/IP has four layers: application, transport, internet, and link. Application protocols like HTTP and DNS ride on TCP or UDP, which ride on IP, which rides on Ethernet or Wi-Fi. It is the practical model; OSI is the teaching model."
Common mistakes
- Saying TCP/IP has five layers without mentioning that some books split link into data link and physical.