The port used by L2TP (Layer 2 Tunneling Protocol) depends on whether it is used with IPSec.
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L2TP with IPSec: When used with IPSec (which is the most common and secure configuration), L2TP utilizes UDP ports 500 and 4500 along with ESP IP Protocol 50. These are the ports used by IPSec itself. L2TP relies on IPSec for encryption and secure transport.
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L2TP without IPSec: If IPSec is disabled (which is strongly discouraged for security reasons), L2TP uses UDP port 1701. This configuration provides no encryption, making the connection vulnerable to eavesdropping and data breaches.
Here's a breakdown in table format:
| Protocol Configuration | Port(s) Used | IP Protocol(s) Used | Security |
|---|---|---|---|
| L2TP with IPSec | UDP 500, UDP 4500 | ESP IP Protocol 50 | High |
| L2TP without IPSec | UDP 1701 | N/A | Low |
Therefore, to summarize: If you are using L2TP with IPSec, the relevant ports are UDP ports 500 and 4500, and ESP IP Protocol 50. If, against best practice, you are using L2TP without IPSec, the port is UDP 1701.
