Common Network Protocols Overview
What are Network Protocols?
Network protocols are standardized rules and conventions that enable computers and devices to communicate across networks. They govern how data is formatted, transmitted, received, and processed.
Most protocols operate at specific OSI or TCP/IP layers, working together as stacks.
Example: HTTP uses TCP, which uses IP.
Transmission Control Protocol (TCP)
Type: Connection-oriented, reliable
- Establishes connection via three-way handshake
- Guarantees data delivery with retransmission and acknowledgments
- Maintains packet order
Use Cases: Web browsing (HTTP/HTTPS), email (SMTP/IMAP/POP), file transfers (FTP), remote logins (SSH)
Example: When John opens https://example.com, his browser uses TCP for reliable communication.
User Datagram Protocol (UDP)
Type: Connectionless, best-effort
- No connection setup, faster transmission
- No guarantees on delivery or order
- Lower overhead than TCP
Use Cases: Streaming (YouTube, Netflix), online gaming, DNS queries, VoIP calls
Example: John’s VoIP phone uses UDP to send voice packets, trading some reliability for lower latency.
Internet Protocol (IP)
Type: Network Layer protocol
- Provides logical addressing (IPv4/IPv6)
- Handles packet routing between networks
Example: John’s PC (192.168.1.10) sends packets to an Internet web server using IP addresses.
Address Resolution Protocol (ARP)
Type: Link Layer protocol
- Maps IP addresses to MAC addresses
- Operates within a LAN
Example: When John pings 192.168.1.20, his PC uses ARP to find the MAC address of that device.
Domain Name System (DNS)
Type: Application Layer protocol
- Resolves human-readable domain names to IP addresses
- Hierarchical structure: root, TLD, authoritative servers
- Supports multiple record types: A, AAAA, MX, CNAME, etc.
Example: John enters www.google.com; DNS translates it to an IP address.
Dynamic Host Configuration Protocol (DHCP)
Type: Application Layer protocol
- Automatically assigns IP addresses and other network config (gateway, DNS)
- Lease process involves DISCOVER, OFFER, REQUEST, ACK messages
Example: John’s laptop connects to Wi-Fi and receives an IP via DHCP.
Hypertext Transfer Protocol (HTTP/HTTPS)
- HTTP: Plain web communication on port 80
- HTTPS: Encrypted web communication on port 443 (uses TLS/SSL)
Example: John browses https://news.com using HTTPS for secure communication.
File Transfer Protocol (FTP)
Type: Application Layer protocol
- Transfers files between computers
- Supports active and passive modes
Example: John uploads files to a website using FTP client software.
Simple Mail Transfer Protocol (SMTP)
Type: Application Layer protocol
- Sends emails
- Works with POP/IMAP for email retrieval
Example: John’s email client uses SMTP to send messages.
Internet Control Message Protocol (ICMP)
Type: Network Layer protocol
- Used for diagnostics and error reporting
- Tools like ping and traceroute use ICMP
Example: John runs ping google.com to test connectivity.
Routing Protocols
Interior Gateway Protocols (IGP)
- RIP: Simple distance-vector protocol, suitable for small networks
- OSPF: Link-state protocol, scalable and fast convergence
- EIGRP: Cisco proprietary, hybrid routing protocol
Exterior Gateway Protocol
- BGP: Used for routing between ISPs and large networks on the Internet
Secure Protocols
- SSH (Secure Shell): Secure remote access and command execution
- TLS/SSL: Cryptographic protocols used in HTTPS, SMTPS, FTPS
Example: John uses SSH to securely manage a Linux server.
Other Common Protocols
- SNMP (Simple Network Management Protocol): For monitoring and managing network devices
- NTP (Network Time Protocol): For synchronizing clocks across devices
Key Points & Exam Tips
- Know common protocol names, port numbers, and use cases.
- TCP vs UDP: TCP is reliable and connection-oriented; UDP is faster and connectionless.
- Understand DHCP, DNS, and ARP for IP management and resolution.
- ICMP is vital for network troubleshooting.
- Use secure protocols (SSH, HTTPS) to protect sensitive data.
- Learn when and why to use specific protocols (FTP for file transfer, SMTP for email, SNMP for monitoring).
Examples Table
| Protocol | Layer | Port | Purpose / Use Case | Example |
|---|---|---|---|---|
| TCP | 4 (Transport) | Varies | Reliable communication | Web browsing (HTTP) |
| UDP | 4 (Transport) | Varies | Fast, connectionless communication | VoIP, streaming |
| IP | 3 (Network) | — | Routing and addressing | Internet packet delivery |
| DNS | 7 (Application) | 53 | Domain name resolution | Accessing websites |
| DHCP | 7 (Application) | 67/68 | Dynamic IP assignment | Wi-Fi client joins |
| ICMP | 3 (Network) | — | Diagnostics, error reporting | ping, traceroute |
| SMTP | 7 (Application) | 25 | Sending emails | Email client to server |
| FTP | 7 (Application) | 21 | File transfer | Uploading web files |
| SSH | 7 (Application) | 22 | Secure remote management | Server admin |
| SNMP | 7 (Application) | 161 | Network management | Switch monitoring |