[core] Feedback on DNS over CoAP - draft-lenders-dns-over-coap

[Martine Sophie Lenders <[e-mail]>]

Dear CoRE-WG,

we would like to present our proposal for DNS over CoAP (DoC):

https://datatracker.ietf.org/doc/draft-lenders-dns-over-coap/

DoC allows for the sending of DNS messages over CoAP, using GET, POST,
and FETCH methods. Similar to DoH in the wider Internet, DoC aims for
providing encrypted DNS message exchange but for constrained IoT
devices, utilizing DTLS or OSCORE,

Comments on our proposal are very welcome! Specifically, we would like
to discuss the following items:

1. How should caching hints in DNS (TTL) relate to CoAP (Max-Age) and
vice versa? How should relative times be handled in general when using
caching [1]? Christian Amsüss previously kicked this discussion off on
the CoRE mailing list [2].

2. Should we only specify the usage of FETCH and abandon GET and POST in
DoC [3]?

   (a) GET introduces the disadvantage that all requested data (such as a
DNS query) needs to be carried within the URI, so block-wise transfer is
not possible. Additional overhead occurs since the data needs to be
converted into a URI format.

   (b) POST, on the other hand, does not allow for en-route caching of
successful responses. In contrast to HTTP, however, CoAP provides the
FETCH method, which allows for both adding data to the body of a request
and caching of successful responses.

   (c) There is one concern regarding FETCH. Various CoAP implementations
do not support FETCH [4] (maybe because FETCH was added later to CoAP).
This could hinder deployment of DoC or could lead DoC implementations
that are not spec-compliant, because implementers just use GET or POST
when FETCH is not available.


Looking forward to your feedback!

Thanks,
Martine
on behalf of the co-authors of draft-lenders-dns-over-coap

[1]https://github.com/anr-bmbf-pivot/draft-dns-over-coap/issues/5
[2]https://mailarchive.ietf.org/arch/msg/core/CzRQTARwPgIwJN0s_kmlLRCNMKY
[3]https://github.com/anr-bmbf-pivot/draft-dns-over-coap/pull/8
[4]https://coap.technology/impls.html