Computer network architectures rely on strict layered abstractions. Whether mapped across the conceptual OSI 7-Layer Reference Model or the industry-standard TCP/IP 4-Layer Suite, protocols interact through structured packet headers, well-defined port assignments, and standardized encapsulation boundaries.
This master cheat sheet catalogs 55+ essential network communication protocols, covering the Application, Transport, Internet, and Data Link layers, alongside RFC standards and default port numbers.
🔗 Related Cheat Sheets: Network Security Protocols & Defensive Architecture Cheat Sheet · Cryptography Algorithms Master Cheat Sheet · HTTP Status Codes Cheat Sheet
1. TCP/IP 4-Layer vs. OSI 7-Layer Protocol Suite Architecture
| TCP/IP 4-Layer Suite | OSI 7-Layer Reference Model | Protocol Data Unit (PDU) | Core Responsibilities | Key Protocols |
|---|---|---|---|---|
| Application Layer | 7. Application 6. Presentation 5. Session |
Message | User/application interface, data formatting, session state management, and RPC | HTTP, HTTPS, DNS, DHCP, SSH, FTP, SMTP, IMAP, MQTT, WebSocket, gRPC |
| Transport Layer | 4. Transport | Segment / Datagram | Process-to-process communication, multiplexing, error checking, flow/congestion control | TCP, UDP, SCTP, QUIC (HTTP/3) |
| Internet Layer | 3. Network | Packet | Host-to-host logical addressing, routing path selection, and packet forwarding | IPv4, IPv6, ICMP, IGMP, IPsec, OSPF, BGP, RIP, GRE |
| Network Interface Layer | 2. Data Link 1. Physical |
Frame Bit Stream |
Node-to-node framing across physical links, MAC addressing, and medium access | Ethernet (802.3), Wi-Fi (802.11), ARP, VLAN (802.1Q), STP, LACP, PPP |
2. Application Layer Protocols & Standard Ports
| Protocol | Full Name | Transport | Default Port | Mechanism & Characteristics | Production Use Case & Role |
|---|---|---|---|---|---|
| HTTP | HyperText Transfer Protocol | TCP | 80 | Stateless ASCII request/response protocol | Plaintext web traffic and unencrypted RESTful APIs |
| HTTPS | HTTP Secure | TCP | 443 | HTTP over TLS/SSL encryption | The universal security standard for modern web traffic |
| FTP | File Transfer Protocol | TCP | 20 (Data) 21 (Control) |
Dual-port architecture; plaintext control commands | Legacy file transfers (largely superseded by SFTP) |
| SFTP | SSH File Transfer Protocol | TCP | 22 | Encrypted file subsystem running over an SSH transport channel | Production Linux file transfers and CI/CD artifact deployments |
| TFTP | Trivial File Transfer Protocol | UDP | 69 | Minimal lock-step file protocol with zero authentication | Network hardware firmware flashing and PXE network booting |
| SMTP | Simple Mail Transfer Protocol | TCP | 25 (Plain) 465/587 (TLS) |
Server-to-server email forwarding and client dispatch | Global internet email routing and automated transactional emails |
| POP3 | Post Office Protocol v3 | TCP | 110 (Plain) 995 (SSL) |
Offline client email retrieval; downloads and purges server copy | Simple personal email client mailbox retrieval |
| IMAP | Internet Message Access Protocol | TCP | 143 (Plain) 993 (SSL) |
Two-way state-synchronized remote mailbox management | Modern multi-device email synchronization (Gmail, Outlook) |
| DNS | Domain Name System | UDP/TCP | 53 | Distributed hierarchical naming resolution; uses TCP for zone transfers | The root address directory of the internet |
| DHCP | Dynamic Host Configuration Protocol | UDP | 67 (Server) 68 (Client) |
Automated dynamic IP, gateway, and DNS configuration leasing | Enterprise LANs, Wi-Fi onboarding, and cloud virtual VPCs |
| SSH | Secure Shell | TCP | 22 | Cryptographic remote command execution, port tunneling, and SFTP | Remote administration of Linux/Unix servers and bastion hosts |
| Telnet | Telecommunication Network | TCP | 23 | Unencrypted plaintext terminal emulation | Legacy device consoles; modern use restricted to raw TCP port testing |
| SNMP | Simple Network Management Protocol | UDP | 161 (Poll) 162 (Trap) |
Tree-structured MIB OID polling and asynchronous telemetry alerts | Network switch, router, and enterprise UPS monitoring |
| NTP | Network Time Protocol | UDP | 123 | Jitter-compensated clock synchronization using stratum hierarchies | Timestamp alignment for financial systems and database consensus |
| LDAP | Lightweight Directory Access Protocol | TCP | 389 (Plain) 636 (SSL) |
Hierarchical X.500 directory tree querying | Enterprise Single Sign-On (SSO) and Active Directory auth |
| RDP | Remote Desktop Protocol | TCP/UDP | 3389 | Proprietary graphical desktop sharing with audio/clipboard channels | Windows Server remote administration and VDI instances |
| VNC | Virtual Network Computing (RFB) | TCP | 5900 | Framebuffer-level cross-platform remote GUI desktop streaming | Remote desktop support across macOS, Linux, and specialized appliances |
| SMB / CIFS | Server Message Block | TCP | 445 | LAN filesystem sharing, file locking, and printer sharing | Corporate shared drives and NAS network storage |
| NFS | Network File System | TCP/UDP | 2049 | Stateless remote UNIX filesystem mount protocol | Kubernetes shared volumes, high-performance compute (HPC) clusters |
| SIP | Session Initiation Protocol | UDP/TCP | 5060 (Plain) 5061 (TLS) |
Multimedia VoIP signaling, session establishment, and teardown | IP telephony, video conferencing backbones (Zoom, Teams) |
| RTP / RTCP | Real-time Transport Protocol | UDP | Dynamic Even/Odd pairs | Low-latency audio/video packet delivery with jitter feedback | Real-time audio/video media transmission in VoIP and WebRTC |
| MQTT | Message Queuing Telemetry Transport | TCP/TLS | 1883 (Plain) 8883 (TLS) |
Lightweight binary Publish/Subscribe messaging with 3 QoS levels | IoT sensor telemetry, connected vehicles, mobile push queues |
| AMQP | Advanced Message Queuing Protocol | TCP/TLS | 5672 (Plain) 5671 (TLS) |
Enterprise programmable message broker protocol with exchanges/queues | Distributed asynchronous decoupling pipelines (RabbitMQ) |
| Redis | REmote DIctionary Server (RESP) | TCP | 6379 | Human-readable binary-safe serialized in-memory protocol | Ultra-fast distributed caching, session storage, and rate limiting |
| MySQL / PG | Database Wire Protocols | TCP | 3306 (MySQL) 5432 (Postgres) |
High-efficiency stateful binary tabular query protocols | Enterprise relational database connection pooling and transactions |
3. Transport Layer Protocols
| Protocol | Connection Type | Reliability & Guarantees | Ordering & Retransmission | Congestion / Flow Control | Primary Workloads |
|---|---|---|---|---|---|
| TCP | Connection-Oriented | Guaranteed delivery via 3-way handshake and ACK sequences | Strictly in-order; automatic selective retransmission (SACK) | Sliding window flow control; dynamic congestion algorithms (BBR, Cubic) | Web browsing (HTTP/1.1, HTTP/2), database queries, file transfers |
| UDP | Connectionless | Best-effort delivery; zero handshake overhead | No ordering; dropped packets ignored | None; application-layer managed | DNS lookups, video streaming, live multiplayer gaming, VoIP |
| QUIC | Connection-Oriented (Over UDP) | Cryptographic handshake + 0-RTT connection resumption | Independent multiplexed streams; zero Head-of-Line (HoL) blocking | Pluggable modern congestion control; connection migration across IPs | HTTP/3 web standard, modern mobile video streaming |
| SCTP | Connection-Oriented | Multi-homing support with multi-streaming architectures | Configurable per-stream ordering; message-oriented boundaries | Standard window-based flow and congestion management | Telecom SS7/Sigtran signaling, WebRTC data channels |
4. Internet & Routing Protocols
| Protocol | Layer Scope | Forwarding / Routing Type | Metric / Algorithm | Typical Deployment Environment |
|---|---|---|---|---|
| IPv4 | Network (L3) | 32-bit packet addressing and fragmented hop-by-hop forwarding | TTL hop count | The legacy addressing foundation of the internet |
| IPv6 | Network (L3) | 128-bit hierarchical addressing with simplified fixed headers | Hop Limit; neighbor discovery | Modern 5G networks, cloud data centers, edge mobile devices |
| ICMP | Network (L3) | Out-of-band operational diagnostic signaling | Error codes & Echo Reply | ping (Echo Request), traceroute (TTL Expired), PMTU discovery |
| BGP | Routing (L7/L3) | Exterior Gateway Protocol (EGP) inter-Autonomous System routing | Path-Vector; multi-attribute policies (AS-Path, Local Pref) | Global internet routing between ISPs and multinational networks |
| OSPF | Routing (L3) | Interior Gateway Protocol (IGP) intra-AS link-state routing | Dijkstra shortest path first (SPF); cost based on interface bandwidth | Corporate enterprise campus backbones and data center fabrics |
| IS-IS | Routing (L2/L3) | Link-state interior routing protocol operating natively at L2 | Dijkstra SPF; TLV extensible metadata payloads | Large-scale telecom carrier core networks |
| RIP | Routing (L7/L3) | Distance-vector interior routing protocol | Bellman-Ford; simple hop counts (15 max hops) | Small legacy local area networks |
5. Data Link Protocols & Technologies
| Protocol / Standard | Operating Sub-Layer | Key Mechanism | Addressing Scheme | Primary Scope |
|---|---|---|---|---|
| Ethernet (IEEE 802.3) | MAC / Physical | CSMA/CD collision detection (legacy); full-duplex switching | 48-bit MAC address | Standard wired local area networks and data center fabrics |
| Wi-Fi (IEEE 802.11) | MAC / Physical | CSMA/CA collision avoidance with RTS/CTS reservations | 48-bit MAC address | Wireless enterprise and consumer local network access |
| ARP | Data Link / Network | Dynamic broadcast translation of L3 IPv4 addresses to L2 MACs | IP ➔ MAC binding cache | Local subnet communication on Ethernet networks |
| VLAN (IEEE 802.1Q) | Data Link (L2) | Injects 4-byte 802.1Q tag into Ethernet frames (12-bit VID: 1-4094) | Logical tag ID | Network segmentation, broadcast storm isolation |
| STP (IEEE 802.1D/w) | Data Link (L2) | Spanning Tree algorithm blocking redundant loops dynamically | Bridge ID + Port Priority | Loop-free failover redundancy in switched Ethernet networks |
| LACP (IEEE 802.3ad) | Data Link (L2) | Link Aggregation bundling multiple physical ports into one logical link | Aggregator MAC | Bandwidth aggregation and physical trunk link redundancy |
Quick Reference Summary: Top 20 Universal Ports
Port 20/21: FTP (Data/Control) Port 80: HTTP Port 443: HTTPS
Port 22: SSH / SFTP Port 110: POP3 Port 445: SMB (Active Directory)
Port 23: Telnet Port 123: NTP Port 587: SMTP Submission (TLS)
Port 25: SMTP (Plain) Port 143: IMAP Port 993: IMAPS (SSL)
Port 53: DNS (UDP/TCP) Port 161: SNMP (Query) Port 3306: MySQL
Port 67/68: DHCP (Server/Client) Port 389: LDAP Port 3389: RDP (Windows Remote)
Port 69: TFTP Port 6379: Redis Cache Port 5432: PostgreSQL