Final answer:
The first step of the site-to-site IPsec encryption process is encapsulation, where the original data is encrypted and encapsulated within a new packet for secure transmission.
Step-by-step explanation:
The first step in the site-to-site IPsec encryption process is encapsulation. During encapsulation, IPsec takes the original data packet, encrypts it, and then places it inside a new packet with a new IP header. This new packet is what travels over the internet, ensuring that the contents remain secure from unauthorized access. Encapsulation is crucial as it ensures both the confidentiality and the integrity of the data being transmitted between sites. Encapsulation involves taking the original IP packet and adding an IPSec header and trailer to it.