Network Protocols
Application Layer Protocols
| Protocol | Port | Transport | Purpose |
|---|---|---|---|
| HTTP | 80 | TCP | Web browsing (HyperText Transfer Protocol) |
| HTTPS | 443 | TCP | Secure web browsing (HTTP over TLS/SSL) |
| FTP | 20 (data), 21 (control) | TCP | File Transfer Protocol |
| SFTP | 22 | TCP | Secure File Transfer (over SSH) |
| SSH | 22 | TCP | Secure Shell — encrypted remote access |
| Telnet | 23 | TCP | Remote access (unencrypted — avoid!) |
| SMTP | 25, 587 | TCP | Simple Mail Transfer Protocol — sending email |
| POP3 | 110, 995 (SSL) | TCP | Post Office Protocol — receiving email (downloads) |
| IMAP | 143, 993 (SSL) | TCP | Internet Message Access Protocol — receiving email (syncs) |
| DNS | 53 | UDP/TCP | Domain Name System — name resolution |
| DHCP | 67 (server), 68 (client) | UDP | Dynamic Host Configuration Protocol — IP assignment |
| SNMP | 161, 162 | UDP | Simple Network Management Protocol — network monitoring |
| NTP | 123 | UDP | Network Time Protocol — time synchronization |
| LDAP | 389, 636 (SSL) | TCP | Lightweight Directory Access Protocol — directory services |
| RDP | 3389 | TCP | Remote Desktop Protocol — Windows remote desktop |
Transport Layer Protocols
| Protocol | Description | Key Features |
|---|---|---|
| TCP | Transmission Control Protocol | Connection-oriented, reliable, ordered, flow control, congestion control |
| UDP | User Datagram Protocol | Connectionless, unreliable, fast, low overhead, no flow control |
| SCTP | Stream Control Transmission Protocol | Multi-streaming, multi-homing, combines TCP reliability with UDP features |
Network Layer Protocols
| Protocol | Purpose |
|---|---|
| IP (IPv4/IPv6) | Internet Protocol — logical addressing and routing of packets |
| ICMP | Internet Control Message Protocol — error reporting and diagnostics (ping, traceroute) |
| ARP | Address Resolution Protocol — maps IP address to MAC address |
| RARP | Reverse ARP — maps MAC address to IP address (legacy) |
| OSPF | Open Shortest Path First — link-state routing protocol |
| BGP | Border Gateway Protocol — inter-domain routing (Internet backbone) |
| RIP | Routing Information Protocol — distance-vector routing |
| IGMP | Internet Group Management Protocol — multicast group management |
Data Link Layer Protocols
| Protocol | Standard | Description |
|---|---|---|
| Ethernet | IEEE 802.3 | Wired LAN standard. Uses CSMA/CD. Speeds: 10Mbps to 400Gbps |
| Wi-Fi | IEEE 802.11 | Wireless LAN. 802.11a/b/g/n/ac/ax (Wi-Fi 6) |
| PPP | RFC 1661 | Point-to-Point Protocol — WAN connections |
| HDLC | ISO 13239 | High-Level Data Link Control — WAN protocol |
| Frame Relay | — | WAN packet-switching protocol (legacy) |
| ATM | — | Asynchronous Transfer Mode — fixed 53-byte cells |
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