Question: What is the mandated protocol for transporting CMPv2 messages between network elements and Registration Authority/ Certification Authority (RA/CA), as per Network Domain Security (NDS) specifications?
Option 1: FTP (File Transfer Protocol) with optional SSL
Option 2: HTTP-based protocol without TLS, with mandatory support for end-entity initiated requests
Option 3: HTTPS (HTTP over TLS) as specified in IETF RFC 2818, with support for both initiated and received communications
Option 4: SMTP (Simple Mail Transfer Protocol) with built-in encryption
Explanation: According to the NDS specifications for CMPv2 transport, HTTP-based protocol is mandated, with a key detail being that support for TLS is not required. Additionally, there's a distinction in the mandatory support based on the initiator of the communication, emphasizing end-entity initiated requests must always trigger a response.