[gtld-tech] A-label and U-label mixing - RDAP query

Thu Apr 14 20:13:48 UTC 2016

From: regext [mailto:regext-bounces at ietf.org] On Behalf Of Gustavo Lozano
Sent: Thursday, April 14, 2016 3:16 PM
To: regext; gtld-tech at icann.org
Subject: [regext] A-label and U-label mixing - RDAP query

Hello colleagues,

Apologies for crossposting.

During the public comments period of the "Registration Data Access Protocol (RDAP) Operational Profile for gTLD Registries and Registrars", https://www.icann.org/public-comments/rdap-profile-2015-12-03-en, the following comment was received:

"Section 1.4.1 of the Operational Profile is inconsistent with the guidance given in RFC 7482 regarding processing of RDAP queries containing a mixture of IDN A-labels and U-labels. Per RFC 7482, "IDNs SHOULD NOT be represented as a mixture of A-labels and U-labels; that is, internationalized labels in an IDN SHOULD be either all A-labels or all U-labels". This requirement is not only inconsistent with RFC 7482, it is also counter to the consensus of the IETF community regarding appropriate processing of IDN queries. "

Another comment on the same path says:

"Allowing A-labels and U-labels will be particularly unworkable for right to left languages unless the RDAP server introduces arbitrary restrictions. It is important to remember that RDAP is intended for machine-to-machine communication. Since RFC 7482 is very clear on this guidance (do not mix the two) any software client that generates this sort of query is broken. With the relative youth of the RDAP standard there is unlikely to be a large install base of software clients with said broken implementation. If ICANN is aware of a software client that has incorrectly implemented the RDAP standard and is now generating queries which combine A-labels and U-labels then ICANN should take its concerns to the IETF where such challenges are considered as part of any implementation discussion. Enshrining bad practice within the Operational Profile will result in needless future changes to the technology or additional service restrictions."

The comment is related to the following section of the gTLD RDAP profile:

"1.4.1 The RDAP server MUST support Internationalized Domain Name (IDN) RDAP lookup queries using A-label or U-label format [RFC 5890] for domain name and name server objects. The RDAP server MUST accept a mixture of the two (i.e. A-label and U-label format) in the same RDAP lookup query".

The purpose of this message is to obtain feedback from this community regarding this issue. We believe that the following text from RFC 7482 is a requirement for the RDAP client: "IDNs SHOULD NOT be represented as a mixture of A-labels and U-labels; that is, internationalized labels in an IDN SHOULD be either all A-labels or all U-labels.".

RFC7482 provides an example of why a server may receive a mixture of A-labels and U-labels in the query: "It is possible for an RDAP client to assemble a query string from multiple independent data sources.  Such a client might not be able to perform conversions between A-labels and U-labels."

RFC7482 gives two options to the server: "An RDAP server that receives a query string with a mixture of A-labels and U-labels MAY convert all the U-labels to A-labels, perform IDNA processing, and proceed with exact-match lookup.  In such cases, the response to be returned to the query source may not match the input from the query source.  Alternatively, the server MAY refuse to process the query".

We believe that the reasoning in RFC 7482 is sufficient to require gTLD RDAP servers to accept and process a query that mixes A-labels and U-labels.

Question for this community: is the behavior specified in the gTLD RDAP Profile (I.e. requiring processing of queries that mixes A-labels and U-labels) consistent with RFC 7482?

I am the editor of the text that appears in RFC 7482. It was written to reflect guidance we received from Andrew Sullivan, John Klensin, and others - it may be worth asking them directly if they're not still following along. It was also discussed during the IESG review. This wasn't an easy topic to wade through.

Having said that, I do believe that the profile requirement that a server MUST support mixed-label lookups is inconsistent with RFC 7482. The text in Section 3.1.3 is clear on the guidance to server operators. As you quoted above:

"An RDAP server that receives a query string with a mixture of A-labels and U-labels MAY convert all the U-labels to A-labels, perform IDNA processing, and proceed with exact-match lookup.  In such cases, the response to be returned to the query source may not match the input from the query source.  Alternatively, the server MAY refuse to process the query."

The RFC says that the server operator can choose which action to perform: convert to all A-labels and process, or refuse to process. Processing a mixture of the label forms isn't one of the available options.

Scott
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mm.icann.org/pipermail/gtld-tech/attachments/20160414/f8511b4f/attachment.html>