Followups probably should go to the dnsops mailing list. I got tired of things and went back to the original question, and put together my list of what the "minimum" packets needed for full DNS performance on the modern Internet. It is the minimum, based on the security principle deny everything, allow only what is needed. But "needed" is performance based. So it means not relying on fallbacks, timeouts or hoping no one complains. It does not include packets needed for diagnostic or troubleshooting information. It is based on the "modern" Internet so does not included very deprecated packets like Source Quench or unimplemented functions like broadcast DNS queries. It does include current Internet practices for EDNS, Notify, global DNS load balancers and error handling I've seen in recent, i.e. less than 10 years old, DNS, Router and OS software. I didn't included TOS/DSCP and some military options, mainly because I'm not sure what "modern" military networks are currently using. If you are using TOS/DSCP or military options, there are some things you will need to add. <http://www.donelan.com/dnsacl.html> <http://www.donelan.com/dnsacl-min-cisco.html>