Are failures cached?

[Mark Andrews]

> We had an issue last week where our Registrar displayed incorrect DNS
> servers for our primary domain for several hours before we realized it
> and corrected the issue.  We're still investigating how the original
> problem occurred but my question isn't about that.   There was no spoof
> site corrected as attempts to resolve our domain website or its MX
> record returned no information as it wasn't on the (wrong) target DNS
> servers.
> The issue was that it appeared many people (including AT&T) seemed to
> fairly quickly get the wrong information so quit sending us email but
> took 2-3 days to get the right information once we'd corrected the
> situation.   Are failures to resolve domains cached?

	Yes.  ~10 minutes.

	Your problem is that the bad delegation records were cached and
	it took some time to flush from caches that learnt the wrong
	values.

	Note: the 2 day TTL.

; <<>> DiG 9.3.4-P1 <<>> water.com @a.gtld-servers.net
; (2 servers found)
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7566
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 2

;; QUESTION SECTION:
;water.com.			IN	A

;; AUTHORITY SECTION:
water.com.		172800	IN	NS	dswadns1.water.com.
water.com.		172800	IN	NS	dswadns2.water.com.

;; ADDITIONAL SECTION:
dswadns1.water.com.	172800	IN	A	12.44.84.213
dswadns2.water.com.	172800	IN	A	12.44.84.214

;; Query time: 373 msec
;; SERVER: 2001:503:a83e::2:30#53(2001:503:a83e::2:30)
;; WHEN: Tue Apr 29 10:13:21 2008
;; MSG SIZE  rcvd: 105

	Mark

> If so are they
> cached longer than actual domain records?  Would the TTL for the wrong
> DNS server be used for a domain for which it wasn't authoritative when
> determining how long to keep a cached record?
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org