>
> In your experience, what's the "longest" a DNS cache is configured to
> keep outdated information? A day? A week? A month? Longer?
>
That is controlled by the TTL (time to live) entry. A DNS server must
refresh it's cache within the TTL for the entry. Using the '-a' option
to host will give you more information:
$ host -a microlinux.fr
Trying "microlinux.fr"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2261
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 2
;; QUESTION SECTION:
;microlinux.fr. IN ANY
;; ANSWER SECTION:
microlinux.fr. 86400 IN SOA ns.microlinux.fr. hostmaster.microlinux.fr. 2017070101 10800 600 1814400 10800
microlinux.fr. 86400 IN A 195.154.171.195
microlinux.fr. 86400 IN MX 10 mail.microlinux.fr.
microlinux.fr. 86400 IN NS ns.microlinux.fr.
microlinux.fr. 86400 IN NS nssec.online.net.
;; ADDITIONAL SECTION:
mail.microlinux.fr. 86400 IN A 195.154.171.195
ns.microlinux.fr. 86400 IN A 195.154.171.195
The '86400' is the TTL - it's in seconds so that's 24 hours. So it all
depends on what the TTL was set to for your old DNS provider.
TTL is a balance between accuracy and network traffic - most DNS
entries don't change for months, so 24 hours is perfectly acceptable.
If accuracy is an issue while a DNS entry changes, then admins often
reduce the TTL during the transition period.
If a particular host is still serving an old DNS entry from its cache
after a TTL has expired, then it's broken. There's not a lot you can do
other than shout at the hostmaster or wait until its personal view of
the world expires.
P.