TTLs on A records?
barmar at alum.mit.edu
Thu Apr 30 23:43:52 UTC 2009
In article <gtd8nt$1vdr$1 at sf1.isc.org>,
"online-reg" <online-reg at enigmedia.com> wrote:
> Hi All: I'm running Bind 9.5.0-P1 / Fedora on my primary NS.
> Are TTLs on individual A records universally supported?
They're supposed to be. Many DNS-based load balancing systems and
services depend on it.
> I have a domain with a TTL of "3h", and I wanted to route traffic between
> two servers in that domain quickly, so I set the TTL to the A record like:
> www 300 A 126.96.36.199
> ;www 300 A 188.8.131.52
> so I could uncomment one and comment the other to manually switch between
> I've had that setup for several weeks during testing...and I just reversed
> the records, incremented the serial, and reloaded BIND.
> On my secondary NS (Bind 9.5.0-P1 / Freebsd 7), when I dig the "www" record,
> I see the TTL counting down from 300 (Cool!), and after it reaches "0", the
> IP address resets to the new one....perfect!
A slave server is authoritative, not caching, so it shouldn't count down
the TTL at all. Or did you mean something else when you said "secondary
> On my Windows DC (server2008), the change was also picked up after 5
> When I use some other lookup services, however (like samspade.org), the old
> IP address shows up for much longer...like it's caching it and ignoring the
> TTL for the record. Should I expect that behavior?
No. Maybe the web site itself is caching. Try querying your ISP's DNS.
Barry Margolin, barmar at alum.mit.edu
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