alert tcp $EXTERNAL_NET any -> $HOME_NET 53 (msg:"GPL DNS zone transfer TCP"; flow:to_server,established; content:"|00 00 FC|"; offset:15; reference:arachnids,212; reference:cve,1999-0532; reference:nessus,10595; classtype:attempted-recon; sid:2100255; rev:14; metadata:created_at 2010_09_23, signature_severity Informational, updated_at 2019_07_26;)