Re: DNS Query Format

At 11:04 AM 3/24/2005 -0700, Alan Maitland wrote:

> Which IP address?  IP Address in the DNS Query - did you mean 
> response?  The IP address of the requesting party is already known.  Sorry 
> to be obtuse, but I really don't understand what you mean.
As I understand it, an SPF query generated by a receiver does not include 
the sender's IP address in that query. That IP address is passed as one of 
the arguments to the check_host() function, but it is not used when 
check_host() constructs the SPF query.  The DNS server which receives the 
query, therefore has no ability to run the SPF check itself, or to log the 
IP for later forensics, etc.
We reached a consensus that having the DNS server run the check is no 
advantage, and forfeits a major benefit of DNS, having the receiver cache 
the response.  If the DNS server responds with only "That IP is good.", the 
answer is not as useful as "Here are all my authorized IPs.  Don't ask 
again for 24 hours."
We haven't yet decided if the remaining small benefit of sending an IP in 
the query is worth the small price of changing the spec to add a few bytes 
of new information.
I hope I got this right. :>)

-- Dave


> At 09:21 AM 3/24/2005, you wrote:
>
> > > > It has been mentioned that the %{i} macro could be included in the 
> > > > query, and then the server could reply with PASS/FAIL. I think this is 
> > > > a bad idea, because all those queries are uncacheable, so this truly 
> > > > circumvents the benefits that were designed into DNS. When the DDOS 
> > > > attempt does happen, caching can really help lower the impact. It may 
> > > > be that I didn't understand the proposal well enough.
> > > Good point.  I hadn't thought of that.  Also, since the PASS/FAIL 
> > > response takes the same single IP datagram as a list of IPs, there is 
> > > not much to be gained.
> > One more thought on this topic:  Even though we see no advantage now in 
> > having a DNS server reply with a PASS/FAIL, would it be a good idea to 
> > include the IP address in the DNS query anyway?  That will add a 
> > negligible 4 bytes to the query, and will allow for some future use of 
> > this information.  This might be, for example, a daemon that alerts a 
> > domain owner when an IP in their domain attempts an unauthorized use of 
> > the domain name. ( A zombie catcher !! )
> > I raise this question now, because it will be a lot easier to modify the 
> > standard now than later.
> > -- Dave
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