wrong RD/RA flags cause exim4 to fail if no MX Record for a domain is set

[Dr. Volker Jaenisch]

Hello Sam!

Thank you for this fast reply.

Sam Trenholme wrote:
> As an aside, RA serves *no* purpose in the DNS header.  There is no
> good reason why clients should look at or care how this bit is set.
> IMHO, Exim is broken because it cares how this bit is set.  I mostly
> fixed this last fall (as you observed); however I didn't cover all of
> the corner cases.
>   
I agree with you that the behavior of exim has to be questioned.
But I disagree with your first point.

RFC 1035 reads:

RA              Recursion Available - this be is set or cleared in a
                response, and denotes whether recursive query support is
                available in the name server.

So RA seems of value if one likes to know wether or not the query has
undergone recursive
treatment or if the DNS-Server supports recursive queries.

I think it is very important to implement the RFC as exakt as possible.
Or lets say the other way around: If an application differs in behavior
from the reference implementation (Bind)
this deviation should be explicitly allowed in the RFC.

RFC 2929 is of no great help :

The AA, TC, RD, RA, AD, and CD bits are each theoretically meaningful
   only in queries or only in responses, depending on the bit.  However,
   many DNS implementations copy the query header as the initial value
   of the response header without clearing bits.  Thus any attempt to
   use a "query" bit with a different meaning in a response or to define
   a query meaning for a "response" bit is dangerous given existing
   implementation.  Such meanings may only be assigned by an IETF
   Standards Action.

In summary it states: There are differences in the implementation of
flags in different DNS servers.

This also promotes my point to implement RFC1035 word by word. :-)

Please do not take this as criticism on maradns. I like to use and
promote maradns. Lets make a better world with better DNS servers. :-)

Best regards,

Volker


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