Meaning of "info: generate keytag query..."

[Matthias Fischer]

Hi,

I run 'unbound 1.7.0' on an IPFire 2.19 / Core 119 firewall router for a
few days. Today I found some messages I never saw before:

...
02:47:12 unbound: [22034:0] info: generate keytag query _ta-4a5c-4f66. NULL IN
14:46:54 unbound: [22034:0] info: generate keytag query _ta-4a5c-4f66. NULL IN
18:38:41 unbound: [22034:0] info: generate keytag query _ta-4a5c-4f66. NULL IN
...

I'd like to know what this means - any hints?

Best,
Matthias