[Changed subject to reflect what we are talking about...]
> On Mar 2, 2020, at 4:16 PM, Rizzo, Christopher <Christopher.Rizzo at xerox.com> wrote:
>> How do you feel about adding the following (first sentence) to your section 4.2 proposal?
I *really* don't want to add this to the beginning of the section. First, that isn't the usual format we use in PWG documents, and second we should focus on what *this* specification requires, *not* what a vendor (Apple) required in their own "standard".
Let's keep working on this:
4.2 DNS Service Discovery (DNS-SD)
DNS Service Discovery (DNS-SD) [RFC6762] uses service (SRV) records and traditional unicast and multicast DNS (mDNS) [RFC6763] queries. Services are identified by a service instance name consisting of a service name, type or sub-type, and domain name. Discovery of Printers is collectively defined in the Bonjour Printing Specification version 1.2.1 [BONJOUR] and extended in this specification.
Printers that support DNS-SD MUST support mDNS and MAY support dynamic DNS updates via Dynamic Updates in the Domain Name System (DNS UPDATE) [RFC2136] and other mechanisms.
4.2.1 History of Printer Discovery with DNS-SD
The Bonjour Printing Specification defines a discovery mechanism for three different printing protocols which are mapped to DNS-SD service types: "_ipp._tcp" for any version of IPP, "_pdl-datastream._tcp" for direct socket communications, and "_printer._tcp" for the Line Printer Daemon (LPD) [RFC1179] protocol. For historical reasons, the primary ("flagship") protocol used for DNS-SD Printer discovery is LPD regardless of whether the Printer actually supports LPD.
DNS-SD makes use of service "sub-types" to identify specific types of services, and the Bonjour Printing Specification also defines a well-known "_printer._sub._http._tcp" service sub-type for a Printer's embedded web server to differentiate a Printer web page from a regular web page.
4.2.2 IPP Everywhere™ Service Sub-Types
In order for a Client to discover IPP Printers that conform to this specification (and not just [STD92]), the following DNS-SD service sub-types are defined:
"_print._sub._ipp._tcp" for IPP Everywhere™ Printers using the "ipp" URI scheme [RFC3510]; and
"_print._sub._ipps._tcp" for IPP Everywhere™ Printers using the "ipps" URI scheme [RFC7472].
4.2.3 Service (SRV) Instance Name
Printers MUST NOT use a service instance name containing a unique identifier by default. A unique identifier MAY be added to the instance if there is a name collision.
The domain portion of the service instance name MUST BE "local." for mDNS.
Printers that support DNS-SD MUST advertise the "_ipp._tcp" (generic IPP) and "_print._sub._ipp._tcp" (IPP Everywhere™) services over mDNS. For example, a Printer named "Example Printer" would have the service instance names "Example Printer._ipp._tcp.local." and "Example Printer._print._sub._ipp._tcp.local.".
Printers that support DNS-SD and the "ipps" URI scheme [RFC7472] MUST advertise the "_ipps._tcp" (generic IPPS) and "_print._sub._ipps._tcp" (IPP Everywhere™ Secure) services over mDNS. For example, a Printer named "Example Printer" would have the service instance names "Example Printer._ipps._tcp.local." and "Example Printer._print._sub._ipps._tcp.local.".
> Note: The IPP Everywhere required "_print._sub._ipp._tcp" and "_print._sub._ipps._tcp" advertisements, which are used to distinguish between legacy IPP and IPP Everywhere support, should not be confused with "_printer._tcp" and "_printer._sub._http._tcp" advertisements referenced in [BONJOUR]. The first version of the Bonjour Printing Specification was published by Apple shortly after the Internet Printing Protocol was published by the IETF. As the Line Printer Daemon Protocol [RFC1179] was considered the most popular network printing protocol at the time, the "_printer._tcp" DNS-SD service type (LPD) was assigned as the "flagship" protocol for DNS-SD advertisements. Similarly, the HTTP service registration for the embedded web server uses the "_printer._sub._http._tcp" service type, even for IPP Printers.
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Michael Sweet
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