Common Network Protocols and Their Functions Explained

Network protocols are the rules that devices use to talk to each other over the internet. They work in layers to handle the data and make sure it reaches its destination securely. For your convenience, here’s a quick walkthrough of networking protocols. 

• Working: They format, send, and interpret data. For these layered models, i.e., OSI (7 layers) and TCP/IP (4 layers), are used. 
• Types: Networking protocols are typically categorized into: application layer protocols, transport protocols, internet layer protocols, and routing protocols. 

• Application protocols are meant to handle daily tasks. For example:
  • • DNS for finding websites
    • FTP for file transfers
    • SMTP/POP3/IMAP for handling emails
    • HTTP for web browsing
    • DHCP for handling IP addresses
    • NTP for time synchronization
    • SSL/TLS & SSH for security purposes
• Transport layer protocols are responsible for ensuring end-to-end delivery of data packets. For example:
  • • TCP for ensuring reliable delivery
    • UDP for handling/improving the speed of the data transfer
• Internet layer protocols are responsible for addressing and routing data packets across different networks. 
  • • IP for addressing devices
    • ARP for linking IPs to devices
    • ICMP for checking errors and ping
    • IPsec for security
• Routing protocols, such as OSPF, BGP, and RIP, determine how data travels across networks and the Internet.

These protocols form the backbone of networking. They make sure your emails, websites, videos, and apps run smoothly all the time.

• Network Protocols - They are referred to as the sets of standardized rules, data structures, and guidelines. These protocols define how data on a network will be formatted, transmitted, and interpreted between devices. In simple terms, they dictate how the devices will communicate (exchange data) across networks.

Regardless of the infrastructure or design, devices that fail to understand the language of these protocols (for any reason) will fail to communicate over a network (both local and global). 

In this blog post, we will be talking about the common types of networking protocols. But before that, let’s have a small eye on how these protocols actually work. 

How Do Network Protocols Work?

As we mentioned in the beginning, networking protocols are a set of rules that define certain elements, such as:

1. How data is packaged (format/structure of messages).
2. How data is transmitted (timing, speed, reliability).
3. How data is interpreted (meaning of signals/commands).

Networking doesn’t rely on a single protocol. It works by organizing information into layers, each serving a separate purpose. Usually, the layers come from the two models:

1. Open System Interconnection (OSI), which involves seven (07) theoretical layers. 
2. The Transmission Control Protocol/Internet Protocol (TCP/IP) involves four (04) practical layers. 

For a deeper understanding of networking protocols, consider first understanding the above-mentioned models. For your convenience, we have provided a brief overview of both below. 

I. Open System Interconnection (OSI) Model

The OSI Model is a conceptual framework and has 07 layers. Different protocols operate at each layer to handle specific aspects of communication. 

The following are the seven layers of the OSI Model, along with the protocols associated with each layer. 

• Application Layer: Where users interact. Protocols: HTTP, FTP, DNS, SMTP.

• Presentation Layer: Data formatting, encryption, compression. Protocols: SSL/TLS.

• Session Layer: Manages sessions (i.e., starts, maintains, and ends them). Protocols: NetBIOS, PPTP.

• Transport Layer: Ensures delivery of data. Protocols: TCP (reliable), UDP (fast).

• Network Layer: Routing and addressing. Protocols: IP, ICMP.

• Data Link Layer: Transfers data between devices on the same network. Protocols: Ethernet, ARP.

• Physical Layer: Actual hardware and signals (cables, Wi-Fi, electrical pulses).

According to this model, when data is sent, it moves from the top (application layer) to the bottom (physical layer). And when it comes to receiving the data, the process is reversed, from the bottom (physical layer) to the top (application layer). 

For a better understanding, read here about the OSI Model in detail. 

II. Transmission Control Protocol/Internet Protocol (TCP/IP) Model

The TCP/IP model is simpler than the OSI model. In fact, it is the model that is actually used in real-world networks. This model consists of four layers, as follows:

• Application Layer: Handles user services. Protocols: HTTP, DNS, SMTP.

• Transport Layer: Manages reliability and speed. Protocols: TCP, UDP.

• Internet Layer: Handles addressing and routing. Protocols: IP, ICMP.

• Network Access Layer (Link Layer): Deals with hardware communication. Protocols: Ethernet, Wi-Fi.

Regarding the working of this model, here’s a short overview for your understanding. 

1. Application Layer

When you open a website, the first layer that comes up is the Application layer. This is where the application begins communicating with the network using HTTP (web), DNS (domain name system), and SMTP (email) protocols. 

As an example:

If you searched for google.com, the DNS translates the domain into an IP address. Then, HTTP/HTTPS will be used to request the Google homepage.

2. Transport Layer

The browser uses the transport layer (TCP) to ensure packets are delivered reliably. It is the TCP layer that breaks the data into packets, numbers them, and ensures missing packets are resent.

As an example:

The Google homepage is too big to send at once. TCP cuts it into small chunks (packets), sends them one by one, and reassembles them correctly on your computer.

3. Internet Layer 

This layer determines how data packets are transmitted across servers on the Internet. Regarding our example for Google.com, each of the data packets will get Google’s IP address (destination) and your device’s IP address (source). Routers along the way use this info to forward the packets until they reach Google’s server.

4. Network Access Layer 

This layer physically transfers the data packets. Here, actual hardware transmission is involved. Your computer sends the packets through Wi-Fi (or Ethernet) to your router. The router passes them to your ISP, then to other networks, until they reach Google’s server.

Google’s server processes the request, then sends back the response (Google’s homepage). The same 4-layer process happens in reverse:

Google’s server → Network Access Layer → Internet → Transport (TCP) → Application (your browser).

Lastly, your browser assembles the packets and displays the Google homepage.

For more details or an in-depth understanding, refer to the TCP/IP Model for further information.

Major Types of Network Protocols

So, you have delved into the workings of network protocols. Now is the time to take you through the major types of protocols. Based on their purpose, networking protocols are typically categorized into the following groups.

1. Application Layer Protocols

Application protocols operate at the top layer of the communication stack. This is the stage where applications interact with the network. Application protocols make sure services like web browsing, email, and file transfers work smoothly. 

Some of the commonly used application protocols include:

I. DNS (Domain Name System)

Domain Name System, also known as DNS, is often referred to as the "phonebook of the internet." It is an application-layer protocol that helps resolve domain names. 

For your understanding, devices communicate with each other on a network using IP addresses. Remembering IP addresses in bulk is not a trait of humans, and it is indeed difficult to remember them all. 

Whenever you search for something online, let’s say Google.com, the device first sends a request to the DNS server to find the corresponding IP address. Once the IP is found, your device can connect directly to Google’s server. The server responds, and your browser loads the Google homepage.

DNS operates through various types of records stored on authoritative servers, each serving a distinct purpose. To determine what records are present in the DNS setup of a domain name, a DNS lookup is performed. 

• A Record (Address Record): Maps a domain name to an IPv4 address.
• AAAA Record: Same as an A record, but for IPv6 addresses.
• CNAME (Canonical Name): Creates an alias for another domain name.
• MX (Mail Exchange): Defines mail servers for handling emails.
• NS (Name Server): Points to the authoritative DNS servers for the domain.
• TXT Record: Stores text information (often used for email verification like SPF, DKIM, DMARC).
• PTR Record (Pointer): Used for reverse DNS lookup (IP → domain name).
• SRV Record: Defines services like VoIP or IM servers. 

II. FTP (File Transfer Protocol)

FTP is another widely used networking protocol. It is designed for transferring files between devices and the network. Here’s how:

1. A client (like FileZilla or WinSCP) connects to an FTP server using login credentials (username and password).
2. The server verifies the user and establishes a connection.
3. Files can now be uploaded (client → server) or downloaded (server → client).
4. After the transfer is complete, the connection is closed.

FTP uses two separate channels for communication. One is a command channel that sends commands and receives responses (such as "upload this file"). Second is the data channel that is actually used for transferring files. 

Here we would like to mention a notable thing that is important for you to know. 

The traditional FTP protocol sends data as plain text. They are not so secure. Many businesses now utilize FTP Secure, which incorporates SSL/TLS encryption into standard FTP to enhance security. 

Sometimes SFTP (SSH File Transfer Protocol) is used, which runs over SSH, offering a completely different but more secure way to transfer files.

III. SMTP (Simple Mail Transfer Protocol)

SMTP is among the most widely used email protocols. Email servers are using them to send email messages in the following sequence or its reverse:

• Client → Email Server → Receiving Email Server. 

You can check the functionality of Simple Mail Transfer Protocol using the SMTP checker tool. 

Do not get confused about the SMTP server, as it is the one that controls how clients receive emails. They just manage how clients send messages. In short, think of it like a mail delivery protocol that only plays a role in sending the messages, not in retrieving them. 

SMTP protocols do not work alone; they work in conjunction with other protocols, such as Post Office Protocol 3 (POP3) or Internet Message Access Protocol (IMAP). These are the ones that control how the mail server receives email messages sent from the client. 

IV. POP3 (Post Office Protocol v3)

As we mentioned earlier, POP3 is an email retrieval protocol. Acting as a post office, this protocol brings the emails from the server to your device. 

Here’s how it works in practice:

Your email client (e.g., Outlook, Thunderbird, or a mobile mail app) connects to the mail server using the POP3 protocol. The protocol downloads all the new emails from the server to your device. Once the emails are downloaded, they are removed from the server (by default).

This means that your emails live locally on your computer or phone. That is why POP3 is a good choice if you want offline access or are working on a single device.

However, POP3 also has a limitation. 

Since emails are deleted from the server after download (unless you tweak the settings), you can’t sync your mailbox across multiple devices. 

For example, if you open an email on your laptop, you won’t see it later on your phone.

In short, the POP3 protocol is suitable for single-device use and offline storage. When the need is for multi-device syncing or shared access, this protocol cannot be used. 

V. IMAP (Internet Message Access Protocol)

IMAP was designed to overcome the limitations of POP3. Instead of pulling emails off the server and storing them locally, IMAP keeps your emails on the mail server and syncs them across devices.

For example:

If you read an email on your smartphone, the same email will show up as “read” when you check it later on your laptop.

That’s why IMAP is the preferred protocol today, especially for people who access their email on multiple devices (phone, tablet, computer).

VI. HTTP (Hypertext Transfer Protocol)

HTTP is the backbone protocol of the World Wide Web. Whenever you open a website, your browser and the web server communicate through the HTTP protocol.

Here’s how it works:

• When you type a URL, such as Google.com, into your browser, your device sends an HTTP request to the server. 
• The server receives this request, processes it, and then sends back an HTTP response with the requested content (like text, images, or scripts). 
• Next, your browser interprets the response and displays the webpage. 
• Along with every request and response, there are HTTP headers. They are actually small pieces of information that provide extra details about the communication.
• HTTP Headers control caching and load speed. They are meant to deliver content in the correct language and format, and identify server issues or misconfigurations. 

You can inspect the headers being sent by using the online HTTP Header Checker. Networking professionals and developers often use them to check whether caching or cookies are working correctly. 

VII. SNMP (Simple Network Management Protocol)

The SNMP protocol is used for collecting and managing information from network devices, such as:

• Routers
• Switches
• Servers
• Printers
• Firewalls

It operates on a manager-agent model, where a manager (typically a monitoring tool) requests data from an agent. The agent (software on the device) responds with details such as CPU load, memory usage, or network statistics.

VIII. DHCP (Dynamic Host Configuration Protocol)

The DHCP protocol is meant to automate the process of assigning IP addresses to network endpoints for each new device that gets connected to the network. These IP addresses establish communication between the devices on the network. 

Without DHCP, you must manually assign an IP address to each new device that connects to your network. For your understanding, here is how the DHCP protocol communicates with devices:

1. Once a device establishes a connection, it sends a DHCP broadcast request on the local network to find available IP addresses. 
2. DHCP server responds with multiple available IP addresses. 
3. The device chooses an address, and a request is made to the DHCP server. 
4. If the server approves the request, it records details such as the device's IP address, MAC address, subnet mask, and hostname. 

Note that the IP address assigned to the device is not permanent; it is leased for a short period only. Once the lease time reaches 50%, the device begins asking for a lease renewal. 

IX. NTP (Network Time Protocol)

NTP ensures that all devices on a network keep accurate and synchronized time. It is constructive for tracing security incidents. Many of the certificates and encryption protocols also rely on correct timestamps. 

Without NTP, one server might log an event at 10:00:02 while another logs the same event at 09:59:58/ This can create confusion while troubleshooting or auditing network errors.

X. SSL/TLS (Secure Sockets Layer / Transport Layer Security)

SSL and its successor, TLS, are both encryption protocols. These protocols are designed to secure communication between a client and a server. They are primarily used in HTTPS to protect online traffic. 

For protection purposes, they encrypt the data in transit while maintaining the integrity and confidentiality. 

To verify whether a website is using SSL correctly, you can use SSL Certificate Checker. It helps confirm if the certificate is valid, properly installed, and not expired, ensuring that the connection is truly secure.

SSL/TLS protocols are among the essential ones, as they also protect sensitive information (e.g., passwords, payment details) from being intercepted by external actors. 

XI. SSH (Secure Shell)

SSH protocols are used to send commands to a device over an insecure network while establishing a secure connection. To protect communication from tampering or dropping, SSH creates an encrypted digital tunnel between devices. For this purpose, they use cryptography for authentication. 

XII. Telenet

The Telenet protocol is particularly designed for remote connectivity purposes. While enabling a remote session, this protocol facilitates the establishment of connections between the remote endpoint and the host machine. 

It is the Telenet protocol that asks users to log in while connecting to a remote network. As the user logs in, the protocol provides them access to the network and its resources. 

However, there is an important thing you should be aware of. Telenet is no longer commonly used due to its security vulnerabilities. Actually, this protocol transfers data in plaintext, including usernames and passwords, which is not a secure option in networking. Nowadays, networking professionals use this protocol occasionally to:

• Test network connectivity
• Check open ports (for remote servers)

2. Transport Layer Protocols

XIII. TCP (Transmission Control Protocol)

TCP is a connection-oriented protocol that helps ensure reliable communication between two devices on the Internet. 

The process begins with a three-way handshake:

• SYN (synchronize) request from the client.
• SYN-ACK acknowledgment from the server.
• ACK confirmation from the client.

Once this handshake is complete, the connection is established, and data can flow.

Remember the transfer of small data packets we mentioned earlier; once an IP address delivers them, the Transmission Control Protocol arranges them in order. 

TCP protects the receiver from being overwhelmed by flow control. Plus, it also plays a vital role in the retransmission of lost packets until delivery is confirmed. 

XIV. UDP (User Datagram Protocol)

The User Datagram Protocol (UDP) is a connectionless protocol that serves as an alternative to TCP. Under this protocol, there is no guarantee that your message will arrive; that is why it is a bit risky. However, setting aside the risk, this protocol comes into use when speed and efficiency are crucial. 

With UDP, data is sent in small packets called datagrams. If some are lost, the sender won’t resend them like TCP. Therefore, loss of data packets is accepted in UDP, and it does not organize the data packets in sequence. 

3. Internet Layer Protocols

XV. IP (Internet Protocol)

IP is the protocol that handles addressing and routing packets across networks. They are unique to devices connected to a network individually. By performing the IP lookup process online, you can easily check your IP address. 

Internet Protocol is like the postal service, where every data packet must carry a source and destination address so it knows where to go. IP addresses usually are of two types: IPv4 and IPv6. 

IP itself doesn’t guarantee delivery (that’s TCP’s job). It simply moves packets from point A to point B using routers along the way.

XVI. ARP (Address Resolution Protocol)

ARP protocol works within LANs (local area networks). They are responsible for mapping IP addresses and the MAC addresses so the devices can communicate. 

FYI, devices communicate using IP addresses, but the actual hardware uses MAC addresses. 

So, when a device wants to communicate with another in the same network:

Let’s say your computer needs to send data to the printer on your local network; it uses ARP to determine the physical MAC address of the device. 

The ARP resolution process does not come into practice during every communication. It comes in practice when a new device joins the network. The future communications are carried out using the associations in the ARP cache. 

XVII. ICMP (Internet Control Message Protocol)

ICMP is used for diagnostics and error reporting while acting as a supporting protocol at the Internet layer of the TCP/IP model. Routers and devices use ICMP to communicate about the network health and trace connectivity issues. 

You may have heard about the IP ping test, which helps determine whether a device's IP address is reachable and measures the response time. 

Moreover, Traceout is used to find the path through which network requests, or data packets, are routed. 

XVIII. IPsec (Internet Protocol Security)

IPsec is a protocol suite used to secure communication over IP networks. It provides encryption, authentication, and integrity for data packets at the network layer. IPsec mainly works in two modes: 

• Transport Mode, which encrypts only the data inside each packet.
• Tunnel Mode, which encrypts the entire packet (commonly used in VPNs). 

The IPsec protocol helps ensure secure communication between devices or entire networks. It is often used for VPNs, site-to-site connections, and protecting sensitive data in transit.

4. Other Protocols

XIX. OSPF (Open Shortest Path First)

OSPF is a routing protocol that determines the best path for data by using a link-state routing algorithm. This protocol is designed to assist IP to send packets on the fastest possible route. 

OSPF is the protocol that establishes the shortest/fastest route for packets to travel. After deciding the path, it updates routing tables (a set of rules that control the movement of data packets). 

The OSPF networking protocol is used only when changes in network routing tables are required or occur. 

XX. BGP (Border Gateway Protocol)

BGP is another network protocol that manages the routing of data packets between different networks and systems. This protocol is also referred to as the path vector. 

Unlike OSPF, it does not route packets along the shortest path. Instead, this protocol routes the data based on policies and rules rather than just distance. 

In short, the BGP protocol is responsible for exchanging information between neighboring routers and ensuring the Internet works properly. 

XXI. RIP (Routing Information Protocol)

RIP is one of the oldest routing protocols. This protocol is also involved in determining the path for data packets. For this, it uses hop count (number of routers a packet passes through) as its metric to choose the best path. 

RIP protocol is simple to configure, but it is limited because it only supports up to 15 hops, making it unsuitable for large networks.

Wrapping Up

Above, we have discussed 21 standard networking protocols. You can think of these protocols as the backbone of communication across devices and networks. They help ensure secure data transfers, manage the routing of data packets, and maintain connectivity. 

Each protocol plays a unique role in keeping the digital world running smoothly. By understanding them and their functions, you gain clearer insight into how everyday online interactions work.