IPsec

Correct Answer: Compression

Compression is the best answer because it reduces the size of data packets, leading to less overhead during transmission over the VPN. It is particularly useful when dealing with high volumes of traffic during peak hours. Replay protection, IPv6, and Perfect forward secrecy are important components of IPsec, but they don't directly address the issue of reducing overhead. Replay protection helps prevent data from being captured and resend, IPv6 relates to the type of IP addresses being used, and Perfect forward secrecy deals with key generation and exchange.

Correct Answer: ESP tunnel mode

The correct choice is 'ESP tunnel mode'. IPsec (Internet Protocol Security) is a suite of protocols used for securing Internet Protocol (IP) communications. It includes both the Encapsulating Security Payload (ESP) and Authentication Header (AH). However, ESP provides both confidentiality (encryption) and integrity protection, while AH only provides integrity protection. When the administrator wants to ensure the confidentiality and integrity of data, ESP should be chosen over AH. Furthermore, the modes of operation include 'transport' and 'tunnel' mode. In transport mode, only the payload of the IP packet is encrypted, leaving the original IP header in clear text. While in tunnel mode, the entire IP packet is encrypted and encapsulated into a new IP packet with a new IP header. This mode is typically used for VPN (Virtual Private Network) over the internet where both confidentiality and integrity of the entire communication are desired, therefore 'ESP tunnel mode' is the best choice. 'ESP transport mode', 'AH tunnel mode', and 'AH transport mode', while providing some level of security, do not meet the full requirement of confidentiality and integrity for transmission of data over the internet.

Correct Answer: RSA digital signatures

The best choice for the authentication method in the IPsec implementation for securing remote connections would be 'RSA digital signatures'. The RSA (Rivest-Shamir-Adleman) digital signatures method relies on the principles of public key cryptography, where two keys are used: a private key that remains secret and a public key that is freely distributed. The receiver can use the sender's public key to verify the authenticity of the message, effectively proving that it was indeed the sender who sent the message, without any need for sharing secret keysAs for the other options, 'DES encryption' is a symmetric key cryptography method, which means it necessitates the sharing of secret keys, hence, it isn't suitable for the described scenario. 'Pre-shared keys' are a method where the same secret key is manually installed on each host - this clearly involves the sharing of secret keys and thus does not meet the team's requirements either. 'Hash-based message authentication code (HMAC)' is a specific kind of message authentication code involving a cryptographic hash function and a secret cryptographic key, the latter indicating again the need for sharing of secret keys.