RR and rrset

[Bob Vance]

Thanks, guys :)

Is it safe to say, then, that all the "RR"s in an "rrset" always have
the same owner name and type?
IOW, would I be correct to say that an "rrset" is that set of all
records that match a given (owner, class, type) triplet?



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BV         | <mailto:BobVance at alumni.caltech.edu>
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-----Original Message-----
From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org]On
Behalf Of Paul Vixie
Sent: Saturday, April 07, 2001 12:44 PM
To: bind-users at isc.org
Subject: Re: RR and rrset


bobvance at alumni.caltech.edu ("Bob Vance") writes:

> What's the difference between the terms
>     "RR"
> and "rrset"
> ?

A resource record (RR) is the indivisible unit of change in DNS.  Here's
an example:

caltech.edu.            2D IN NS        MERCUTIO.NI.caltech.edu.

A resource record set (RRset) is the indivisible unit of transfer in
DNS.
Here's an example, from which the above RR is drawn:

caltech.edu.            2D IN NS        MERCUTIO.NI.caltech.edu.
caltech.edu.            2D IN NS        TEPID.NI.caltech.edu.
caltech.edu.            2D IN NS        TYBALT.caltech.edu.
caltech.edu.            2D IN NS        NSX.LBL.GOV.

By "indivisible" I mean that nothing smaller is ever done.  You can
change
(or add or delete) a single RR but you always transfer (either in a zone
transfer or a query or an update) whole RRsets.  RRsets are said to be
"atomic" which means their TTL (time to live) is "minimized".  If in a
zone
file an RRset is presented with unequal TTL's, then the lowest TTL is
used
for all RRs in the RRset.  If in a DNS cache somewhere an RRset's RRs
have
unequal TTL's, then when the lowest TTL is reached, the whole RRset is
dropped and refetched.