prereq yxrrset problem

[Michael Fuhr]

I've noticed a problem with dynamic updates when using an "RRset
exists (value dependent)" prerequisite and more than one record
of the specified type exists.  Perhaps somebody can tell me if
I'm missing something or if BIND is behaving strangely.

Here's an example that works:

1. The zone example.com has no MX records.  Add one MX record
by feeding the following to nsupdate:

  update add example.com. 3600 IN MX 10 mail1.example.com.

2. Delete the MX record with the following:

  prereq yxrrset example.com. IN MX 10 mail1.example.com.
  update delete  example.com. IN MX 10 mail1.example.com.

3. This update returns NOERROR and the record is deleted.

Here's an example that fails:

1. The zone example.com has no MX records.  Add two MX records
with the following:

  update add example.com. 3600 IN MX 10 mail1.example.com.
  update add example.com. 3600 IN MX 10 mail2.example.com.

2. Issue the same delete command as in the previous example:

  prereq yxrrset example.com. IN MX 10 mail1.example.com.
  update delete  example.com. IN MX 10 mail1.example.com.

3. This update returns NXRRSET and no record is deleted.  The
nameserver (8.2.3-REL) logs the following:

  error processing update packet (NXRRSET) id 34346 from [10.0.0.1].3666

A correspondant reports the same behavior with 9.1.1rc6.  We
can work around the problem by omitting the prerequisite, but
sometimes a prerequisite can be handy and it ought to work as
far as I know.

Am I missing something?  I've been looking through RFC 2136 but
nothing has jumped out at me yet.

Thanks.

-- 
Michael Fuhr
http://www.fuhr.org/~mfuhr/