[Techtalk] Stupid DNS questions

[Mary]

On Mon, Mar 08, 2004, Michelle Murrain wrote:
> I was 
> afraid if for some reason the first became unavailable, the second 
> would then not work, which is then besides the point (which also 
> makes me ponder the issue of the remote slave).

A slave DNS server will continue to serve a zone file for a certain
amount of time after its master becomes available. This time is called
the expiry time, and you can control it via the zone file.

Here's the SOA (start of authority) data for puzzling.org:

$ host -t SOA puzzling.org
puzzling.org            SOA     puzzling.org hostmaster.puzzling.org (
                        2004022801      ;serial (version)
                        10800   ;refresh period (3 hours)
                        3600    ;retry interval (1 hour)
                        3600000 ;expire time (5 weeks, 6 days, 16 hours)
                        86400   ;default ttl (1 day)
                        )

If the master vanishes, the slave will continue making its puzzling.org data
available for 3600000 seconds.

I believe the slaves will attempt to get new zone data as often as the refresh
field (10800 seconds in this case) specifies.

See http://www.ndo.com/ndo/Support/DNS_Guide_-_A_Crash_Course/supdnsguide.html

-Mary