A series of TCP packets are being sent from a DNS server to an external webserver over port 53. Based on the information given, what is most likely generating the traffic?

DNS zone transfers are initiated over TCP port 53 because TCP provides the reliable, ordered delivery needed to transfer a complete zone file from a primary to a secondary DNS server. Standard DNS queries and responses use UDP port 53 for efficiency. Traffic originating from a DNS server over TCP port 53 to an external host is a strong indicator of zone transfer activity.

DNS queries are directed to DNS resolvers or authoritative servers, not web servers, and typically use UDP rather than TCP port 53.

Whois lookups use TCP port 43, not port 53, and are initiated by clients, not DNS servers.

DNS query responses originate from the DNS server back to the querying client using UDP port 53, and a webserver would not be sending DNS queries to a DNS server in normal operation.