What are the key network protocols used in 2025 and how are they categorized across OSI layers?

Network protocols are essential for managing communication between devices in any IT infrastructure. This guide explains the most important network protocols categorized by OSI model layers—Application, Transport, Network, and Data Link. From protocols like TCP and UDP to SNMP, SSH, and Ethernet, this blog breaks down their roles, examples, and security implications in a simple and easy-to-understand format. Whether you're a beginner in networking or preparing for certifications, knowing how these protocols function is crucial for troubleshooting, optimization, and secure network design in 2025.

Network Security Jul 5, 2025 24 Add to Reading List

Network protocols are the rules that allow devices to communicate across networks—from your smartphone connecting to Wi-Fi to routers exchanging data across the globe. These protocols operate at different layers of the OSI model and handle everything from web browsing to secure file transfers.

In this guide, we explain each protocol layer-by-layer, using real-world examples, simple terms, and use cases you can relate to. Whether you're a student, network engineer, or cybersecurity enthusiast, this blog is your go-to reference for understanding how data moves in a network.

What Are Network Protocols?

Network protocols are sets of rules that determine how data is transmitted between devices in a network. Each protocol works at a specific OSI layer, from user applications to the physical wires.

These layers include:

Application Layer
Transport Layer
Network Layer
Data Link Layer

Application Layer Protocols (Layer 7)

This is where users interact with services like web browsing, email, and file transfers.

Protocol	Function	Example
SIP (Session Initiation Protocol)	Sets up video or voice calls	VoIP calls, Zoom
FTP (File Transfer Protocol)	Transfers files between devices	Website uploads
SNMP (Simple Network Management Protocol)	Manages and monitors network devices	Router monitoring
Telnet	Remote access via plain text (not secure)	Legacy router management
SSH (Secure Shell)	Encrypted remote terminal access	Secure server login

Tip: Always use SSH instead of Telnet for security.

Transport Layer Protocols (Layer 4)

This layer ensures that data is delivered correctly or quickly, depending on the use case.

Protocol	Purpose	Use Case
TCP (Transmission Control Protocol)	Reliable, connection-based communication	Email, websites
UDP (User Datagram Protocol)	Fast, connectionless communication	Video calls, games

TCP = Reliable but slower.
UDP = Faster but no delivery guarantee.

Network Layer Protocols (Layer 3)

This layer is responsible for routing data and assigning IP addresses.

Protocol	Role	Common Use
IP (Internet Protocol)	Delivers packets to correct address	All internet traffic
ICMP (Internet Control Message Protocol)	Sends error messages	Ping and traceroute
OSPF (Open Shortest Path First)	Finds best route in large networks	Enterprise routing
EIGRP	Cisco-based hybrid routing protocol	Cisco networks
RIP (Routing Information Protocol)	Basic routing using hop counts	Legacy setups
ARP (Address Resolution Protocol)	Resolves IP to MAC addresses	LAN communication

Ping not working? Check ICMP or firewall rules.

Data Link Layer Protocols (Layer 2)

These protocols manage physical data transmission on local networks.

Protocol	Function	Use
Ethernet	Wired data transmission	Most LANs
HDLC	Point-to-point communication	WAN backbones
PPP (Point-to-Point Protocol)	Adds authentication to links	Dial-up, VPNs
Frame Relay	Packet switching	Replaced by MPLS
LLDP (Link Layer Discovery Protocol)	Device discovery protocol	Shows neighbors on switches

OSI Layers & Key Protocols

Layer	Protocols	Role
Application	SIP, FTP, SNMP, SSH, Telnet	User services
Transport	TCP, UDP	Data delivery
Network	IP, ICMP, OSPF, RIP, ARP, EIGRP	Routing & addressing
Data Link	Ethernet, HDLC, PPP, LLDP	Frame transmission

Real-World Protocol Scenarios

VoIP Call: SIP (setup) + RTP via UDP (audio) + IP (routing)
SSH Login: SSH over TCP to remote Linux server
Router Discovery: LLDP identifies neighbors and ports
Web Download: TCP connection using IP routes
Ping Test: ICMP request to test reachability

Best Practices for Network Protocols

Use SSH over Telnet for secure access
Apply SNMPv3 for encrypted monitoring
Prefer OSPF or EIGRP for scalable routing
Filter ICMP traffic for protection, but allow for diagnostics
Document IP addresses and ARP tables for troubleshooting

Why Protocols Matter for Cybersecurity

Many cyberattacks exploit insecure protocols:

Telnet can leak credentials (use SSH)
SNMPv1 transmits in plaintext (use SNMPv3)
Unfiltered ICMP can expose live systems

Securing protocols = securing your network.

✅ Conclusion

Understanding network protocols helps you:

Diagnose network issues
Secure devices and systems
Build better infrastructure
Pass certifications like CCNA, CEH, and CompTIA Network+

Mastering how protocols work at each layer makes networking less mysterious and more manageable.

FAQs

What are network protocols?

Network protocols are rules that define how data is transmitted between devices in a network to ensure reliable and secure communication.

How many layers are there in the OSI model?

The OSI model has 7 layers, but most protocol discussions focus on the top 4: Application, Transport, Network, and Data Link layers.

Which protocols work at the Application layer?

Common Application layer protocols include SIP, FTP, SNMP, SSH, and Telnet.

What is the difference between TCP and UDP?

TCP is reliable and connection-oriented, while UDP is faster and connectionless but doesn’t guarantee delivery.

What is IP used for?

IP (Internet Protocol) assigns addresses to devices and ensures data packets reach the correct destination.

What does ICMP do?

ICMP is used for sending error and control messages, like in ping or traceroute.

What is OSPF?

OSPF (Open Shortest Path First) is a dynamic routing protocol used in large enterprise networks to find the best path.

What is EIGRP?

EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary routing protocol that combines distance vector and link state features.

What is the role of ARP?

ARP (Address Resolution Protocol) maps IP addresses to MAC addresses so devices can communicate over a LAN.

Why is SSH preferred over Telnet?

SSH encrypts all communication, while Telnet sends data in plaintext, making it insecure.

What does SNMP do?

SNMP is used to monitor and manage network devices by collecting metrics like CPU usage and bandwidth.

What are Data Link layer protocols?

Examples include Ethernet, HDLC, PPP, Frame Relay, and LLDP.

What is Ethernet?

Ethernet is the most common protocol for wired LAN communication.

What is LLDP used for?

LLDP (Link Layer Discovery Protocol) allows network devices to advertise their identity and capabilities.

What is PPP?

PPP (Point-to-Point Protocol) is used for direct connections over serial links and supports authentication.

What is HDLC?

HDLC (High-Level Data Link Control) is a synchronous data link protocol used in WAN connections.

Is RIP still used today?

RIP is outdated but may still exist in legacy networks; modern networks prefer OSPF or EIGRP.

How do I secure network protocols?

Use encrypted versions (e.g., SSH instead of Telnet), block unused protocols at the firewall, and enforce SNMPv3.

What is the function of SIP in networking?

SIP (Session Initiation Protocol) is used to initiate, manage, and terminate voice and video communication sessions.

How is FTP different from HTTP?

FTP is used for file transfers, while HTTP is used for web browsing.

What does the Transport layer do?

It ensures reliable or fast delivery of data depending on the protocol (TCP or UDP).

What is the difference between the Network and Data Link layers?

The Network layer handles routing and addressing, while the Data Link layer handles local delivery of frames.

How do these protocols affect cybersecurity?

Unsecured protocols like Telnet and SNMPv1 can expose networks to attacks; secure versions should always be used.

Are these protocols still used in 2025?

Yes, many of these protocols are foundational and still widely used in both modern and legacy systems.

Which protocols should I focus on for CCNA or CEH exams?

Focus on TCP, UDP, IP, ICMP, OSPF, FTP, SSH, SNMP, and Ethernet for both networking and cybersecurity certifications.

Can these protocols be monitored?

Yes, tools like Wireshark, SolarWinds, and SNMP-based software can monitor protocol traffic and behavior.