[dns-operations] To A or to AAAA - was Re: Signaling client

Doug Barton dougb at dougbarton.us
Tue Jan 18 03:01:49 UTC 2011

On 01/17/2011 13:40, Doug Barton wrote:
> On 01/17/2011 13:28, Edward Lewis wrote:
>> The reason for this rambling tirade is that Doug's part right but falls
>> short when it gets to determining "address records they cannot use."
>> That's impossible to "compute". I might have a v6 set up in my house
>> but be on a ISP that can route me to f.root-server.net/AAAA but not
>> m.root-servers.net/AAAA (I've seen this). An application can't possibly
>> know a priori to ask for f's AAAA and not m's AAAA. Trying both will
>> tell me, but not until I try.
>> Applications need to be more aggressive and rugged in trying to reach
>> whatever they want off the 'net.
> I agree with your thorough response, mine was designed more to indicate
> that the right layer for the solution is _not_ the DNS.
> That said, while I do agree in general that applications/OS' should have
> better heuristics in regard to connectivity I think that it should at
> least be possible for them to be smart enough to know what transports
> they definitely cannot use, and avoid breaking themselves by asking for
> them. :)

To expand on this answer slightly:

Solving this problem in DNS is, quite simply, a bad idea. And it's a bad 
idea for any number of reasons, including but not limited to:

1. It requires (or may require, depending on what layer you solve it at) 
OS vendors, many of whom are not directly affected by the problem, to 
invest time and money into fixing it.
2. It requires (or may require, depending on what layer you solve it at) 
network operators to upgrade their resolving name servers.
3. The spec for the solution won't be finished before IPv6 is already 
widely deployed (that's only sort of a snark).
4. To the extent that end users update their software at all, they 
_tend_ to update applications more than the OS. Although to be fair, the 
constant harping about windows users doing windows update has improved 
this to some extent. But the real, dirty truth is that most users don't 
update anything, ever.
5. Application developers are (or can be) much more nimble in this 
regard, and since we're all in agreement that this is where the real 
solution should be anyway ...



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