Bind 8.2 with non Bind 8.2 interoperability + AA flag

[Marc Lampo]

Hello and my best whishes to all,

Hopefully somebody can enlighten me on 2 points :
1. I'm puzzled about the cooperation between Bind 8.2 and others with
respect to $TTL.
When performing a zone transfert and obtaining a zone from a
bind8.2 server (with named-xfer)
I notice :
- the $TTL value appears explicitly on each record, except for the SOA
- the "ttl" from the SOA record is in the SOA itself and appears as ttl
for that record
The same operation on a bind8.1.2 server reveals :
- the "ttl" from the SOA is everywhere (in the SOA and as ttl for all
records)

So I've already learned (but should have guessed) that the $TTL is
merely a local syntax for Bind8.2
and the line itself is not sent over the network.  But then, how  can a
Bind8.2 slave for a non Bind8.2
master "know" that a negative cache time of 10 minutes (the build in
default prior to bind8.2) should
be given in its replies ?

2. While looking into packets to try and puzzle out point 1 myself,
I also noticed the AA flag is
always set in replies with rcode == NXDOMAIN.  Even if this answers
comes from a caching only
name server.
And the AA flag is also set in replies from a caching only name server
if that server had to lookup the
answer itself (ttl values being identical to the ones in the
SOA record).
It strikes me as odd because I'd just read the passage in O'Reilly's
book stating that the AA flag
gives an indication of the authority of the replying name server with
respect to the domain queried for.

Thanks for any clarifying answer,

Marc Lampo

-- --
Security Engineer for C-CURE CBVA, Belgium
Guest teacher of Client/Server Programming @ AT Computing (Dutch only)
Opionions are strictly personal and do not commit either company