What does IPsec do in a VPN architecture?

In a VPN architecture, IPsec primarily functions to encrypt communications. This makes it especially valuable for securing data as it travels across potentially vulnerable or untrusted networks, such as the internet. By encrypting the data packets, IPsec ensures that the information remains confidential and is only accessible to authorized parties who possess the correct decryption keys. This encryption process not only protects the integrity of the data but also provides authentication, ensuring that the data originates from a legitimate source and has not been altered during transmission.

While the other options may represent functions relevant to networking, they do not accurately reflect the primary role of IPsec in a VPN context. IPsec does not assign IP addresses; that function typically falls to protocols such as DHCP. Similarly, route discovery is managed by routing protocols rather than IPsec. Lastly, controlling bandwidth usage pertains to traffic shaping or Quality of Service (QoS) measures, which are outside the direct capabilities of IPsec. Therefore, the essence of IPsec in a VPN is firmly rooted in its ability to provide encryption for secure communication.