[dns-operations] finding the longest encloser

Jim Reid jim at rfc1035.com
Tue Feb 16 23:50:24 UTC 2010

On 16 Feb 2010, at 22:27, Crist Clark wrote:

>> The SOA record does not contain the longest existing suffix.  I think
>> you really need to know that the root is delegation-centric, or that
>> all delegations have a single label, combined with the SOA trick to
>> deal with the arpa. special cases.
> Shouldn't it always contain the longest valid zone? I mean, that's
> what it's there for right?

Yes and no. Once upon a time, I was co-author of a draft that  
suggested using the SOA record in an NXDOMAIN response to find the  
closest enclosing delegation. This was to be used in ENUM domain names  
with ~20 labels and could have contain a handful of delegations:  
walking up the domain name label at a time to find the deepest  
delegation point (=> "closest" default SIP/PSTN terminator) would have  
been painful.

I was told that this was too clever by half and it wasn't acceptable  
for clients to treat SOA records in this way because they were in the  
Authority Section. Clients were supposed to only act on whatever was  
in the Answer Section.

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