Underscore prefix names are entirely user convention the same way as 
IN-ADDR.ARPA and IP6.ARPA are user convention.  There is NOTHING in resolvers 
or name servers that treat these names as special in any sort of way what so 
ever.

gethostbyname and getnameinfo just implement the user convention. 

ksk-sentinel requires validating recursive servers to have different code paths 
for names that start with these labels.  That makes them special.

As for nothing breaks if you don’t implement, that is true of most/all names in 
the special use registry to exactly the same extent as not implementing 
ksk-sentinel doesn’t break anything.


> On 16 May 2018, at 3:24 am, Ted Lemon <mel...@fugue.com> wrote:
> 
> Hm, well, the analogy I was making is that this is essentially a signal to an 
> application, which happens to be a caching name server.  "Other name servers 
> treat them as ordinary names" is not a reason not to list a special-use name 
> in the registry.   Ideally we want names like this to have as small an 
> implementation footprint as possible.   The reason I am objecting to the idea 
> that this is a special-use name is that it doesn't seem fundamentally 
> different to _tcp, aside from the detail of what software happens to consume 
> it.   Special-use names do generally require special treatment by the system, 
> even though we hope that the footprint will be as small as possible.   Right 
> now entries in the table are either not global names (which doesn't apply 
> here) or are intended for special purposes (e.g., example.com, invalid), or 
> require a protocol other than DNS to resolve (local, onion).
> 
> The case for handling this as a special-use name is that we'd want 
> implementors of naming software to find it in the registry so that they'd 
> know to do it, but I don't think that applies here—the downside to not doing 
> it is that you don't get the new feature, not that something breaks.   That's 
> very similar to the downside of not knowing what _tcp means.
> 
> On Tue, May 15, 2018 at 12:39 PM, Matthew Pounsett <m...@conundrum.com> wrote:
> 
> 
> On 15 May 2018 at 12:34, Tony Finch <d...@dotat.at> wrote:
> Ted Lemon <mel...@fugue.com> wrote:
> 
> > It might be useful to compare this to labels like _tcp that appear in SRV
> > records and elsewhere.
> 
> The reason for listing a name in the RCF 6761 registry is because it needs
> special handling of some kind in DNS software. That isn't the case for the
> _underscore names, which (from the DNS point of view) are just ordinary
> domain names that have conventional uses in applications.
> 
> I'm going to suggest a modification to your first sentence.  The reason for 
> listing a name int he RFC 6761 registry is because it needs special handling 
> of some kind in DNS software that would otherwise be unaware of the special 
> handling required by that name.  In this case, the only name servers that 
> need to handle these names specially are the ones implementing the 
> technology.. all other name servers treat them as ordinary names.
> 
> 
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: ma...@isc.org

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