What feature enhances the security of a connection in IPsec by providing an additional verification step?

The feature that enhances the security of a connection in IPsec by providing an additional verification step is the use of digital signatures. Digital signatures serve as a means of ensuring integrity and authenticity in data transmission. In the context of IPsec, digital signatures allow the receiving party to verify that the data has not been altered during transmission and confirm the identity of the sender. This additional layer of security is crucial in defending against various types of attacks, such as replay attacks, where an unauthorized party might attempt to intercept and resend packets.

While encryption of the data payload is significant for protecting the confidentiality of data, it does not inherently involve verification of the sender’s identity or the integrity of the data. Symmetric keys are fundamental to the encryption process, providing a means for both ends to encrypt and decrypt messages, but they do not address the authenticity or integrity of the data. NAT traversal is a technique that helps IPsec work through NAT devices, but it is not directly related to enhancing security through verification. Thus, the use of digital signatures stands out as the key feature enhancing the security of an IPsec connection through an additional verification step.