How to send an update to servers that cached my dns info

[Barry Margolin]

In article <9m4730$30d at pub3.rc.vix.com>,
Marc Logemann <logenews1 at morelogs.de> wrote:
>I just read something in "DNS and BIND" (ORA) about the SOA record,
>and about "refresh" they say:
>
>"The refresh interval tells the salve how often to check thats its
>data are up to date...."
>
>About "TTL" they ay:
>
>"This value applies to all resource records in your .db file. The name
>supplies this TTLs in queriy responses, allowing other server to cache
>the data for the TTL intervall"
>
>1. question: When i say 600 seconds TTL and i make a change in my zone,
>is it wrong to say that after 600 secs other servers must re-query my
>nameserver for correct adress?

The time doesn't start when you make the change.  When a server caches one
of your records, it must discard that record after 600 seconds, and if it's
queried for the record again it must re-query one of the authoritative
servers for the domain.

>2. question: What does the "refresh" do? i cant get it from the book,
>perhaps i am dumb but anyway :)

Slave servers periodically query the master server to find out if their
copy of the zone is out of date.  The timing of these queries is controlled
by the "refresh" and "retry" parameters.  Every "refresh" period the slave
will ask the master for the SOA record of the zone, and check whether the
master's serial number is higher than the serial number it already has; if
so, it will perform a zone transfer to get a new copy of the zone.  If an
error occurs while querying for the SOA record or trying to transfer the
zone, the slave then performs this process every "retry" period until it
succeeds, and then it goes back to using the "refresh" period.

Note that TTL has no effect on slave servers, it's only used by caching
servers.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Woburn, MA
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