DNS problems to RoadRunner - tcp vs udp

Mark Price mprice at tqhosting.com
Fri Jun 13 13:11:11 CDT 2008


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



>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
the answer is over a certain length.


Any clues would be appreciated.



Mark



-- 
Mark Price
Tranquil Hosting
www.tqhosting.com




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