DNS servers optionally log queries on demand by formatting a message and storing that in a file, sending it through syslog, etc. This is an I/O-intensive operation which can dramatically slow down busy servers, and the biggest issue is we get the query but not the associated response. [1505125481] unbound[89142:0] info: 127.0.0.2 dnstap.info. A IN 10-Sep-2017 08:31:03.644 client @0x7f9b12dd5c00 12