On Mar 4, 2011, at 8:29 PM, Fred Baker wrote:

> On Mar 4, 2011, at 5:15 PM, Keith Moore wrote:
> 
>> How is my laptop, when it does the DNS dynamic update, supposed to know that 
>> it has an external address, and what that address is, so it can include an 
>> AAAA record for it?
> 
> I spent a lot of time on that in an earlier email, one you chose to not 
> respond to.

Oh, sorry.  I did see that message.  But sometimes I spend hours composing 
message responses, so longer messages take longer to respond to.  And sometimes 
it's hard to know what context 

> There are two ways: 
> 
> (a) it reports the address it knows, and the DNS server infers the other 
> addresses, or
> (b) it sends an ICMP request to a multicast address, collects zero or more 
> responses, and reports what it collects.

I like (b).  It works with DNS update (assuming that can be made to work) but 
it's not limited to DNS - any application that does referrals can use it.   It 
can be implemented in the host, and separately, in the application - without 
their interfering with each other.  It makes it possible to ship apps that do 
the right thing in a variety of environments.  Let's design it in detail.

As for (a) I don't think that a DNS server should infer that just because an 
update request comes in from a different address than specified in the AAAA 
record, that it should add an additional AAAA record based on the source 
address of the request.  Partly because the server has no reason to believe 
that the host actually wants that address advertised, and partly because it 
appears that some CPEs intercept DNS queries and proxy DNS updates.  (The data 
sheet for the new DSL modem that my current ISP just sent me touts this feature 
without explaining it, which makes me think that it might be a common feature.)

Keith

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