TCP/IP Model·Lesson 8 of 8
Protocols Used in Each Layer
A Protocol for Every Job
Each layer of the TCP/IP model comes with its own set of — the agreed rules that get that layer's job done. Higher layers deal with what the data means (a web page, an email), while lower layers deal with how it travels (addresses, signals). This lesson gathers the most important protocols and pins each one to the layer it belongs to. Getting these mappings straight is one of the most common networking interview checks.
The interview favourite
Expect to be asked "which layer does HTTP (or IP, or Ethernet) work at?" Memorize the layer for each major protocol and you'll answer these instantly.
Application Layer Protocols
The top layer holds the protocols that applications speak directly — for browsing, email, file transfer, naming, and remote access. These are the names you meet most often as a developer:
| Protocol | Full name | What it does |
|---|---|---|
| HTTP / HTTPS | HyperText Transfer Protocol (Secure) | Requests and delivers web pages; HTTPS adds encryption |
| DNS | Domain Name System | Turns names like example.com into IP addresses |
| SMTP | Simple Mail Transfer Protocol | Sends email between mail servers |
| IMAP / POP3 | Mail access protocols | Let your mail app fetch and read messages |
| FTP | File Transfer Protocol | Transfers whole files between client and server |
| SSH | Secure Shell | Encrypted remote command-line access |
| DHCP | Dynamic Host Configuration Protocol | Automatically assigns IP addresses to devices |
Transport Layer Protocols
The transport layer has just two protocols worth memorizing — but they matter enormously. One trades speed for reliability; the other does the opposite:
| Protocol | Full name | What it does |
|---|---|---|
| TCP | Transmission Control Protocol | Reliable, ordered, connection-oriented delivery |
| UDP | User Datagram Protocol | Fast, connectionless, best-effort delivery |
Internet Layer Protocols
The internet layer is built around IP, with a few companions for diagnostics and group communication. These handle addressing and routing rather than the content of the data:
| Protocol | Full name | What it does |
|---|---|---|
| IP | Internet Protocol (IPv4 / IPv6) | Addresses and routes packets across networks |
| ICMP | Internet Control Message Protocol | Carries error and diagnostic messages (used by ping) |
| IGMP | Internet Group Management Protocol | Manages membership in multicast groups |
Network Access Layer Protocols
The bottom layer holds the technologies that carry frames over a physical link and the helpers that keep a local network working. ARP is a special case — it bridges IP addresses to hardware addresses, so it sits right at the boundary of this layer:
| Protocol | Full name | What it does |
|---|---|---|
| Ethernet | IEEE 802.3 | Carries frames over wired LAN connections |
| Wi-Fi | IEEE 802.11 | Carries frames over wireless connections |
| ARP | Address Resolution Protocol | Maps a known IP address to its MAC address |
| PPP | Point-to-Point Protocol | Carries frames over a direct link between two devices |
The Whole Map at a Glance
Putting it all together, here's the entire TCP/IP stack with the key protocols sitting at each layer. This single picture is the fastest way to revise the whole topic:
Protocols by TCP/IP layer
Application
HTTP, HTTPS, DNS, SMTP, IMAP, POP3, FTP, SSH, DHCP
Transport
TCP, UDP
Internet
IP, ICMP, IGMP
Network Access
Ethernet, Wi-Fi, ARP, PPP
“"TCP and IP are at the same layer — that's why we say 'TCP/IP'."”
Q:Which layer does HTTP work at, and which does IP work at?
A: HTTP is an application-layer protocol — it's what apps use to request web pages. IP is an internet-layer protocol — it addresses and routes packets across networks. HTTP data is carried by TCP at the transport layer, which in turn is carried by IP below it.
Quick Revision Cheat Sheet
Application: HTTP, HTTPS, DNS, SMTP, IMAP, POP3, FTP, SSH, DHCP
Transport: TCP (reliable), UDP (fast)
Internet: IP, ICMP, IGMP
Network Access: Ethernet, Wi-Fi, ARP, PPP
Common trap: TCP and IP are different layers, not the same one