Which protocol is used for secure DNS communication in FortiGate configurations?

The protocol used for secure DNS communication in FortiGate configurations is DNS over TLS. This protocol provides an encryption layer for DNS queries, which helps maintain privacy and integrity by preventing eavesdropping or manipulation of DNS data during transmission.

When DNS over TLS is implemented, it establishes a secure connection between the client and the DNS server, allowing DNS queries and responses to be transmitted securely. This is particularly important in modern network security practices, where keeping DNS traffic secure can help protect against various attack vectors, like spoofing or man-in-the-middle attacks.

In contrast, while other options like DNS over SFTP and DNS over HTTP exist or may relate to securing data traffic, they are not standard or widely recognized protocols specifically used for DNS queries. Traditional DNS uses UDP, but this does not provide security features, making it unsuitable for secure DNS communication purposes. Thus, DNS over TLS stands out as the correct answer in FortiGate configurations for secure DNS communication.