I have hundreds of lines like this in my syslog from many different ip addresses:
Oct 16 17:03:06 example named[857]: client @0x7fa2dc083e40 104.190.220.183#3075 (sl): query (cache) 'sl/ANY/IN' denied
Oct 16 17:03:06 example named[857]: client @0x7fa2d812bc70 90.196.21.194#80 (sl): query (cache) 'sl/ANY/IN' denied
a reverse dns on 104.190.220.183 gave Hostname: 104-190-220-183.lightspeed.tukrga.sbcglobal.net. a reverse dns on 90.196.21.194 gave Hostname: 5ac415c2.bb.sky.com.
What is this hacker trying to achieve and should I be concerned as the attempt is denied?