Questions about "incomplete" additional data

[Matt Larson]

At the risk of displaying my ignorance of BIND internals, I have some
questions about how BIND behaves when receiving an incomplete list of A
records in the additional section of a referral.

For example, let's say that in the process of resolving www.foo.us/IN/A, a
BIND server sends that query to a root name server and receives this
referral:

; Authority
us.     in  ns  ns1.foo.us.
us.     in  ns  ns2.foo.us.
us.     in  ns  ns1.bar.net.

; Additional
ns1.foo.us. in  a   1.2.3.4
ns2.foo.us. in  a   1.2.3.5

In other words, there's no A record for ns1.bar.net included in the
additional section.  And this is a new enough server so that TC isn't set on
this reply.  My questions are:

- When does a BIND server resolve ns1.bar.net/IN/A--immediately upon receipt
of the referral, or does it wait until it actually needs to send a query to
ns1.bar.net?

- Are the name servers whose A records are present in the additional section
"favored" in any way?  For example, would ns1.foo.us and ns2.foo.us each
receive more queries than ns1.bar.net?

- Is BIND's behavior in this situation consistent across all (most?)
versions?  Do some versions of BIND have drastically different behavior than
others in this regard?

Thanks to those who can read the source better than I for any insight.

Matt
--
Matt Larson <mlarson at netsol.com>
Network Solutions Registry / www.nsiregistry.com