Application-Layer Traffic Optimization (ALTO) Cross-Domain Server Discovery
draft-ietf-alto-xdom-disc-06

Thank you for educating me :-) 
(previous position was discuss because I didn't understand the deployment scenario).

I concur with Alissa's comment.

Section 6.4: It seems that people's understanding of the kind of threat described in this section has changed somewhat since 2009 when RFC 5693 was published. For example, work to provide confidentiality protection for DNS client requests to recursive resolvers (DoT and DoH) has occurred in the time since then, and the information revealed by such requests is arguably less sensitive than the information sent by ALTO clients. I don't know if the applicability of DoT/DoH to NAPTR has been written about anywhere, but at a minimum it seems that this is worthy of some discussion here.

Thanks for a very readable draft, especially given the that we are talking about naptr stuff :-)

I agree with Alissa's comment.

§2, 4th paragraph: "The service parameter SHOULD always be set to "ALTO:https"."
That SHOULD is redundant to the similar requirement in §3.1. Since that section describe the detailed procedures, I suggest leaving the normative keywords to it, and using descriptive language here.

Thank you for the updates; they have captured enough of the discussion we had
to clarify that most of my points of concern are either non-concerns or have
adequate workarounds.

I'm still not entirely sure that DNSSEC in the reverse zone is available everywhere
in a robust fashion, but it seems that there is enough availability that the mechanisms
specified here can still be used in a useful manner.

However, I do think that we need to clarify in Section 5.2.2 that this mechanism is
compatible with the BCP 20 sub-allocation scheme only insamuch as you can add
NAPTR records in the relevant locations -- the current procedures described in the
text will not catch everything just on their own, IIUC.

Also, one nit in Section 2: s/is usually always be set/is usually set/

In this text, 

   One such scenario is detailed in
   Appendix C.

there are several scenarios in Appendix C. I THINK you may want me to look at Appendix C.3, which is an example, which is fine, but whether that's what you want me to look at or not, it would be useful to point more specifically at what you're thinking about.