From what I have read, public DNS servers should support both UDP and TCP queries. TCP queries are often used when a UDP query fails, or if
I have seen intermittent problems on some client windows servers sending to rr.com recently. For example, the MX hosts for triad.rr.com are: # dig -t mx triad.rr.com ;; QUESTION SECTION: ;triad.rr.com. IN MX ;; ANSWER SECTION: triad.rr.com. 1609 IN MX 10 hrndva-smtpin01.mail.rr.com. triad.rr.com. 1609 IN MX 20 hrndva-smtpin02.mail.rr.com. The authoritative nameservers for mail.rr.com: # dig -t ns mail.rr.com ;; QUESTION SECTION: ;mail.rr.com. IN NS ;; ANSWER SECTION: mail.rr.com. 14204 IN NS cdptpa-admin02.mail.rr.com. mail.rr.com. 14204 IN NS hrndva-admin01.mail.rr.com. mail.rr.com. 14204 IN NS hrndva-admin02.mail.rr.com. mail.rr.com. 14204 IN NS cdptpa-admin01.mail.rr.com. All 4 of those queries will answer a UDP DNS query for host record hrndva-smtpin01.mail.rr.com. However, the hrndva-admin01.mail.rr.com and hrndva-admin02.mail.rr.com servers do not respond to TCP queries at all. Example: # dig hrndva-smtpin01.mail.rr.com @hrndva-admin01.mail.rr.com +tcp ; <<>> DiG 9.3.3rc2 <<>> hrndva-smtpin01.mail.rr.com @hrndva-admin01.mail.rr.com +tcp ; (1 server found) ;; global options: printcmd ;; connection timed out; no servers could be reached the answer is over a certain length. Any clues would be appreciated. Mark -- Mark Price Tranquil Hosting www.tqhosting.com