On 2009-01-29 at 14:01 +0100, Florian Weimer wrote:
* Mark Andrews:
The most common reason for recursive queries to a authoritative server is someone using dig, nslookup or similar and forgeting to disable recursion on the request.
Useful to know, thanks. So someone performing diagnostics on one of the root/gTLD/ccTLD servers would need to remember to dig +norec when checking visibility? Are manual diagnostics going out from the source IP of such auth nameservers considered common? In any case, it's a small enough, and hopefully clued enough, sample of admins that it shouldn't be a problem. Any organisation seeking to add their auth nameservers to a public RBL of such IPs will have to accept the same constraint on needing clued staff. No tears shed at that.
dnscache in "forward only" mode also sets the RD bit, and apparently does not restrict itself to the configured forwarders list. (This is based on a public report, not on first-hand knowledge.)
Unless any of the root/gTLD/ccTLD nameservers are also running dnscache, it should be safe to drop UDP RD packets from those source IP addresses, as previously described. -Phil