4.4BSD/usr/src/contrib/bind-4.9/contrib/umich/SA_records

Update 9-9-92

named now supports a '-s' flag.  Using it means that your secondary server
supports shuffle A records, and so when sending them via the zone transfer
mechanism, it will send a "SA' record instead of a plain "A" record.

It also handles the case where a give domain name has some SA records and
other types of records.  (It shuffles the A records and leaves the rest
alone.)

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SA records are a new data type that I have added to BIND 4.8.3.  They are
"shuffle A records".  They look and act just like A records except the
nameserver shuffles them up before replying to the requester.

Use SA records in cases where you would like several A records returned, but in
a different order each time.  There is no support in SA records for any kind of
scheduling or weighting; you're stuck with randomness.

The syntax of a SA record is identical to the of an A record, except that the
type field is SA, not A.

SA records are implemented in this way.  An additional record type is defined
in /usr/include/arpa/nameser.h, namely T_SA (104).  In addition a new named
data flag is defined, DB_F_SHUFFLE.

db_load() is modified to recognize SA records.  When it finds one, it sets
the DB_SHUFFLE data flag of the record, but then it falls through to the
standard A record code.  From this point on only your nameserver knows it
is a SA record; to the rest of the world (including your secondary servers)
it will apeear as an A record (EXCEPTION: if you use the -s flag described
above).

ns_req() and ns_resp() also need to be modified to check to see if the
DB_SHUFFLE flag is set on any data they are to return.  If they do see
the flag, then all of the A records with that flag set are shuffled.

The shuffling is handled by a routine called shuffle_rrs() in a new
source file ns_shuf.c.  The shuffling code is simple.  Records are
not so much shuffled as they are re-ordered.

The bind4.8.3.tar.Z release in this directory contains a BIND 4.8.3 with
SA record support.  I would have made some kind of diffs available, but
because of the various versions of BIND floating about (4.8.1, 4.8.3,
patched 4.8.3, patched and hacked 4.8.3, . . .) it really isn't very
easy.

Some future work might include adding SX (shuffle MX) records, getting
the shuffle code to cope with non-A records, and getting named-xfer to
preserve SA records in secondaries.