Network Protocol Reference
Comprehensive guide to network protocols, OSI model, and TCP/IP stack
The OSI Model - 7 Layers
The Open Systems Interconnection model is a conceptual framework that describes how data moves through a network in seven distinct layers.
7
Application Layer
Network process to application
Function:
Provides network services directly to end-user applications
Protocols:
HTTP/HTTPS
FTP
SMTP
DNS
DHCP
SSH
Telnet
SNMP
Devices:
Application Gateways, Proxy Servers
6
Presentation Layer
Data representation and encryption
Function:
Translates data between the application layer and network format
Protocols:
SSL/TLS
JPEG
GIF
ASCII
EBCDIC
Encryption
Compression
Devices:
Encryption Devices, Compression Software
5
Session Layer
Interhost communication
Function:
Establishes, manages, and terminates connections between applications
Protocols:
NetBIOS
SQL
RPC
NFS
SMB
SCP
Devices:
Gateways, Proxy Servers
4
Transport Layer
End-to-end connections and reliability
Function:
Provides reliable data transfer services to the upper layers
Protocols:
TCP
UDP
SPX
DCCP
SCTP
Devices:
Firewalls, Gateways
3
Network Layer
Path determination and logical addressing
Function:
Routes data packets between networks using logical addresses
Protocols:
IP (IPv4/IPv6)
ICMP
OSPF
BGP
EIGRP
RIP
ARP
Devices:
Routers, Layer 3 Switches
2
Data Link Layer
Physical addressing
Function:
Provides node-to-node data transfer and handles error correction
Protocols:
Ethernet
PPP
STP
VLAN
MAC
Wi-Fi (802.11)
ARP
Devices:
Switches, Bridges, Network Cards
1
Physical Layer
Media, signal and binary transmission
Function:
Transmits raw bit stream over the physical medium
Protocols:
Ethernet Standards
USB
Bluetooth
RS-232
RJ45
Fiber Optics
Devices:
Hubs, Repeaters, Cables, Connectors
TCP/IP vs OSI Model
While OSI is a conceptual model, TCP/IP is the practical implementation used in modern networks.
OSI Model (7 Layers)
Application
Layer 7
Presentation
Layer 6
Session
Layer 5
Transport
Layer 4
Network
Layer 3
Data Link
Layer 2
Physical
Layer 1
TCP/IP Model (4 Layers)
Application
HTTP, FTP, DNS, DHCP
Transport
TCP, UDP
Internet
IP, ICMP, ARP
Network Access
Ethernet, Wi-Fi, PPP
Application Layer Protocols
| Protocol | Port | Description | Common Use Cases |
|---|---|---|---|
| HTTP/HTTPS | 80/443 | Web browsing and secure web traffic | Web servers, APIs, web applications |
| FTP/SFTP | 21/22 | File transfer protocol | File uploads/downloads, server management |
| SMTP | 25/587 | Email sending protocol | Email servers, mail clients |
| POP3/IMAP | 110/143 | Email retrieval protocols | Email clients, mailbox access |
| DNS | 53 | Domain name resolution | Name servers, domain lookups |
| DHCP | 67/68 | Dynamic IP assignment | Network configuration, IP management |
| SSH | 22 | Secure remote access | Server administration, secure file transfer |
| Telnet | 23 | Unsecure remote access (deprecated) | Legacy systems (avoid use) |
| SNMP | 161/162 | Network management protocol | Network monitoring, device management |
| NTP | 123 | Network time synchronization | Time servers, clock synchronization |
Routing Protocols
| Protocol | Type | Description | Common Use Cases |
|---|---|---|---|
| OSPF | Link-State | Open Shortest Path First | Large enterprise networks, ISPs |
| BGP | Path-Vector | Border Gateway Protocol | Internet routing, ISP connections |
| EIGRP | Hybrid | Enhanced Interior Gateway Routing Protocol | Cisco networks, enterprise routing |
| RIP | Distance-Vector | Routing Information Protocol | Small networks, legacy systems |
| IS-IS | Link-State | Intermediate System to Intermediate System | ISP networks, large enterprises |
| MPLS | Label Switching | Multiprotocol Label Switching | Service provider networks, VPNs |
Transport Layer Protocols
| Protocol | Type | Description | Common Use Cases |
|---|---|---|---|
| TCP | Connection-oriented | Transmission Control Protocol | Reliable data transfer, web, email |
| UDP | Connectionless | User Datagram Protocol | Real-time applications, DNS, DHCP |
| SCTP | Connection-oriented | Stream Control Transmission Protocol | Telephony signaling, multi-streaming |
| DCCP | Connection-oriented | Datagram Congestion Control Protocol | Streaming media, online games |
| QUIC | Connection-oriented | Quick UDP Internet Connections | HTTP/3, low-latency applications |