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UDP vs TCP: Choosing VPN Protocols on OpenVPN

WRITTEN BY
Timothy Shim
UPDATED
April 23, 2024

 

VPN protocols have been undergoing development for years now and one of the most stable (and successful) is OpenVPN.

 

However, did you know that there’s a difference between OpenVPN TCP and UDP?

 

Although either of them will work with OpenVPN they will have a different effect on your connection. VPN UDP vs TCP come with different speeds and security profiles. Understanding the difference can help you make the right choice in different scenarios.

 

Let’s break it down.

 

 

What is the TCP Protocol?

 

speed test result tcp openvpn

Speed test result for NordVPN when using TCP OpenVPN. (Credit: speedtest.net)

 

TCP is an abbreviation for Transmission Control Protocol. It is a transport layer protocol used in OpenVPN, an open-source Virtual Private Network (VPN) solution that creates secure, encrypted connections over the internet.

 

When used in OpenVPN, TCP is one of the two available options for transmitting data (the other being UDP).

 

TCP is a reliable, connection-oriented protocol, meaning that it establishes a connection between two endpoints before transmitting data. This connection is maintained throughout the entire communication process, and both endpoints exchange control messages to ensure the reliability of the connection.

 

In OpenVPN, TCP is often used when data reliability is a top priority, such as in situations where data loss or corruption could have serious consequences, such as when transmitting financial data or other sensitive information.

 

Advantages of TCP

 

  • Guaranteed delivery of data
    TCP ensures that all data packets are received in the order they were sent, and retransmits any lost packets, making it more reliable than UDP.
  • Compatibility
    TCP is supported by virtually all devices and network configurations, making it a good choice for interoperability with different systems and networks.
  • Security
    TCP’s reliable delivery ensures that no data is lost or corrupted during transmission, making it more secure than UDP, which does not provide the same level of reliability.

 

Disadvantages of TCP

 

  • Slower speed
    TCP’s reliability comes at the cost of slower transmission speeds, as the connection setup and control messages add overhead that can slow down data transfer.
  • Vulnerability to congestion
    TCP is more vulnerable to congestion on the network than UDP, as it relies on a congestion control mechanism that can cause delays if too much data is being transmitted.

 

 

What is the UDP Protocol?

 

speed test result udp openvpn

Speed test result for NordVPN when using UDP OpenVPN. (Credit: speedtest.net)

 

User Datagram Protocol, or UDP, is also a transport layer protocol used in OpenVPN. It is an alternative option for those who prefer not to use TCP in some situations. This protocol is connectionless, meaning that it does not establish a connection between two endpoints before transmitting data.

 

Instead, UDP sends data packets, called datagrams, directly to the destination without any guarantee of their delivery or order. Because of the lack of verification, UDP is faster and more efficient than TCP, but also less reliable.

 

In OpenVPN, UDP is often used when speed and efficiency are a top priority. Many of the fastest VPN speeds are timed when OpenVPN combines with UDP, especially when large amounts of data need to be transmitted quickly.

 

Advantages of UDP

 

  • Faster transmission speeds
    UDP’s lack of connection setup and control messages makes it faster than TCP, as it can transmit data packets more quickly. It’s important to understand that this speed advantage is in the context of OpenVPN. It does not apply when compared to other protocols like WireGuard.
  • Lower latency
    UDP’s lack of reliability means that there is less processing overhead, resulting in lower latency and faster response times.
  • Compatibility
    UDP is supported by virtually all devices and network configurations, making it a good choice for interoperability with different systems and networks.

 

Disadvantages of UDP

 

  • Unreliable delivery
    UDP does not guarantee the delivery of all data packets, and some packets may be lost or delivered out of order.
  • Vulnerability to packet loss
    UDP’s unreliable delivery makes it more vulnerable to packet loss than TCP, especially on congested networks.
  • Security
    UDP’s lack of reliability means that there is no guarantee that all data has been received and processed correctly, making it less secure than TCP.

 

 

Comparing TCP and UDP Protocols in VPNs

 

Although there are similarities between VPN UDP and TCP, there are fundamental differences in their design and functionality.

 

These differences are important when considering specific use-case scenarios even within OpenVPN deployment on a VPN.

 

TCP UDP
Reliability Yes No
Speed Slowed by protocol overhead Fast
Congestion control Includes mechanism forcongestion control No congestion detection
Packet size Better for large packets Better for small packets
Error handling Retransmission None
Resource usage Requires more resources Requires fewer resources

 

Key differences between TCP and UDP

 

  • Reliability
    TCP is a reliable, connection-oriented protocol, meaning that it establishes a connection between two endpoints before transmitting data and ensures that all packets are received in order and without errors. UDP, on the other hand, is an unreliable, connectionless protocol that does not guarantee the delivery or order of packets.
     
    TCP is used in applications that require reliable, ordered, and error-free delivery of data, such as email, file transfers, and web browsing. UDP is used in applications that require fast, real-time communication, such as online gaming, video conferencing, and VoIP.
  • Speed
    UDP is generally faster than TCP because it has less overhead and does not require a connection setup or control messages. However, this comes at the cost of reliability, as some packets may be lost or delivered out of order.
  • Congestion control
    TCP uses a congestion control mechanism that detects network congestion and slows down the transmission rate to avoid congestion, while UDP does not have a built-in mechanism for congestion control.
  • Packet size
    TCP is designed for larger data transfers and can handle packets of up to 64KB in size, while UDP is better suited for smaller packets and has a maximum packet size of 65,535 bytes.
  • Error handling
    TCP uses a mechanism called retransmission to resend any packets that are lost or corrupted during transmission, while UDP does not have a built-in mechanism for error handling.
  • Resource usage
    TCP requires more resources, such as memory and processing power, than UDP due to its connection-oriented design and congestion control mechanism.
     
    Since each protocol offers its own pros and cons, the best VPN service providers will always provide users with access to both.

 

 

Does OpenVPN use TCP or UDP?

 

nordvpn offers tcp udp openvpn

NordVPN offers a choice of OpenVPN with either TCP or UDP.

 

By default, OpenVPN uses UDP as the transport protocol for its VPN connections, but users can choose to use TCP if they prefer.

 

When OpenVPN uses UDP, it typically employs the UDP port number 1194 by default, although this can be changed if necessary. UDP is preferred in OpenVPN for its speed and efficiency, making it a good choice for real-time applications such as video conferencing, online gaming, and VoIP.

 

However, UDP’s lack of reliability can also make it less suitable for certain applications where data integrity is critical. In such cases, TCP can be used instead. When OpenVPN uses TCP, it typically employs the TCP port number 443, which is commonly used for HTTPS traffic.

 

TCP provides a reliable, ordered, and error-free data transfer, making it a good choice for applications that require data integrity, such as email, file transfers, and web browsing. However, TCP also has more overhead than UDP and can be slower in certain situations.

 

Overall, the choice between TCP and UDP in OpenVPN depends on the specific requirements of the application.

 

If speed and efficiency are the primary concerns, UDP is the better choice, but if data integrity and reliability are more important, TCP may be a better option.

 

 

When to Use TCP or UDP?

 

udp vs tcp

 

The differences between TCP and UDP in OpenVPN are clear and contrasting. Because of that, your specific choice depends heavily on the specific application scenario, even within the context of a VPN.

 

Here are some factors to consider when deciding whether to use TCP or UDP in OpenVPN:

 

  1. What are the network conditions?
    If the network is unreliable, congested, or has a high packet loss rate, TCP may be a better option because it provides reliable data transfer with error correction and retransmission. UDP may be a better option when the network is reliable and has low latency and low packet loss.
  2. What are the application requirements?
    If the application requires reliable data transfer and error-free delivery, such as for file transfers, email, or web browsing, TCP is the better choice. If the application requires real-time data transfer and low latency, such as for video streaming, gaming, or VoIP, UDP is the better choice.
  3. Consider firewall and NAT traversal
    Some firewalls and NAT devices may block or interfere with certain types of traffic, such as UDP packets. In such cases, using TCP may be necessary to ensure that the VPN traffic can traverse the network successfully.
  4. What performance do you need?
    UDP is generally faster and has less overhead than TCP, making it a good choice for applications that require speed and low latency. However, TCP may be a better choice for large data transfers because it provides flow control and congestion control, preventing the network from becoming congested.

 

 

Final Thoughts: UDP for Speed, TCP for Reliability!

 

When considering VPN UDP vs TCP I’ve almost always preferred UDP for most scenarios. Although switching between the two is possible, it’s a bit inconvenient and interrupts your Internet experience.

 

Unless you have a specific case when you need every bit of data to come through correctly, there’s no reason to suffer a speed impact by choosing TCP.

 

 

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