The OPT pseudo-record
The OPT (options) record is a pseudo-record that contains extra fields that were added to DNS later. If present, there should only be one of these in a DNS request or response.
dog sends OPT records as part of queries by defaults, but hides them in the response. For more information, see the EDNS section.
Here, we make a standard request to
a-example.lookup.dog, but tell dog to show the OPT record in the response with the
It specifies a UDP packet size of 512, and is in the Additional section.
Because these records do not have a defined domain name or TTL, those values are left blank, and the data is shown in the final column instead.
$ dog a-example.lookup.dog --edns show A a-example.lookup.dog. 1h00m00s 10.20.30.40 OPT + 512 0 0 0