Question about AA bit

[Hideshi Enokihara]

Hi all,

I have one question about the difference of the treatment of AA bit between bind-8 and bind-9.

For example,the following topologys are assumed. 

        AP Server1              DNS Server2
          |A.example.org           |example.org
          |3ffe:501:ffff:101::10   |3ffe:501:fffff:101::20
          |192.168.1.10            |192.168.1.20
          |                        | 
Net-y   --+--------+---------------+---------------------- 3ffe:501:ffff:101::/64
                   |                                       192.168.1/24
                   |
                   |
                 Router
                   |3ffe:501:ffff:100::1
                   |192.168.0.1
                   |
                   |
Net-z   --+--------+-----------------+-------------------- 3ffe:501:ffff:100::/64
          |                          |                     192.168.0/24
          |                          |
        DNS Server1               DNS Cient1
           3ffe:501:ffff:100::XXXX    3ffe:501:fffff:100::20
           192.168.0.10               192.168.0.20
	
In this topology, 1.DNS Client1 send query for QNAME=A.example.org,QTYPE=A to DNS Server1.
And 2.DNS Server1 send (recursive) query to DNS Server2 that is Authority of "example.com".
3. DNS Server2 send response with AA bit=1 to DNS Server1.
I have the question about next response(4). 

   DNS Client1                    DNS Server1                      DNS Server2
        |                              |                                 |
        |----------------------------->|                                 |
        | 1. Send standard query       |                                 |
        |    QNAME=A.example.org       |                                 |
        |    QTYPE=A                   |                                 |
        |                              |                                 |
        |                              |-------------------------------->|
        |                              | 2. Send standard query          |
        |                              |  QNAME=A.example.org            |
        |                              |  QTYPE=A                        |
        |                              |                                 |
        |                              |<--------------------------------|
        |                              | 3. Send standard response       |
        |                              |  QNAME=A.example.org            |
        |                              |  QTYPE=A                        |
        |                              |  ANSWER Name=A.example.org      |
        |                              |  ANSWER Address=192.168.1.10    |
        |                              |  AUTHORITY Name=example.org     |
        |                              |  AUTHORITY Name Server          |
        |                              |            =NS2.example.org     |
        |                              |  ADDITIONAL Name=NS2.example.org|
        |                              |  ADDITIONAL Address=192.168.1.20|
        |                              |                                 |
        |<-----------------------------|                                 |
        | 4. Standard query response   |                                 | 
        |  QNAME=A.example.org         |                                 |
        |  QTYPE=A                     |                                 |
        |  ANSWER Name=A.example.org   |                                 |
        |  ANSWER Address=192.168.1.10 |                                 |
        |  Authority Name=example.org  |                                 |
        |  Authority Name Server       |                                 |
        |            =NS2.example.org  |                                 |
        v                              v                                 v 

If DNS Server1 is bind-8, AA bit of this response(4) is set to 1. 
However, if DNS Server1 is bind-9, AA bit of this response(4) is set to 0. 
Why is the behavior of bind-8 and bind-9 different like this?

What is the reason why behavior is changed like this by bind9?
Is the reason due to RFCs?

Could you teach me?

Best Regards,
-- 
*************************************
Hideshi Enokihara
IPv6 Business
Network & Software Development Dept.
Yokogawa Electric Corporation