l2tp

L2TP (Layer 2 Tunneling Protocol) is a protocol used to support virtual private networks (VPNs) or as part of the delivery of services by ISPs. It does not provide encryption on its own but is often used in conjunction with IPsec for secure communication. L2TP operates on port 1701.

What is l2tp

L2TP, or Layer 2 Tunneling Protocol, is a tunneling protocol used to support virtual private networks (VPNs) or as part of the delivery of services by internet service providers (ISPs). It was developed as a combination of two older protocols: PPTP (Point-to-Point Tunneling Protocol) and L2F (Layer 2 Forwarding Protocol). L2TP itself does not provide encryption or confidentiality, which is why it is often paired with IPsec (Internet Protocol Security) to ensure secure data transmission.

When used in conjunction with IPsec, L2TP/IPsec provides a robust and secure VPN solution. The L2TP protocol handles the tunneling aspect, while IPsec takes care of encryption, authentication, and integrity. This combination is widely used in corporate environments to allow remote employees to securely connect to the company's internal network over the internet.

L2TP operates on port 1701 and is commonly supported by many operating systems and network devices. Its ability to encapsulate multiple protocols makes it versatile for various networking scenarios. Despite its advantages, the reliance on IPsec for security means that proper configuration and management are crucial to prevent vulnerabilities and ensure the integrity of the VPN connection.

l2tp runs on TCP and UDP port 1701 and is official IANA port.

Security risk

If port 1701 is open and the L2TP service is running without proper security measures, it can be exploited by attackers to gain unauthorized access to the network. Ensuring that L2TP is used in conjunction with IPsec and that strong authentication methods are in place is crucial to mitigate these risks.

In our UFW tutorial you can follow instructions how you can configure UFW to close port 1701. Use StackChanges to monitor if the l2tp port is closed and stays closed. StackChanges will send an alert if port 1701 is open again.