Subject: [core] DNS over CoAP: A new Content-Format

From: Martine Sophie Lenders <[email-masked]>
Date: Fri, 25 Mar 2022 12:39:34 +0100

Hi,

during today's meeting, I was asked to put the four discussion points I 
presented in my talk on DoC [1] on the list. Here is the discussion 
points on a potentially new Content-Format (slides 8-9 at [2], maybe 
also 7 for context).

Due to the overhead we face with, e.g., OSCORE and link-layer security, 
we might already run into 6LoWPAN fragmentation. Sure, this could be 
circumvented with block-wise transfer, but it would be better 
performance-wise, to put as much information as possible into one 
message and link-layer PDU. As such, we probably need some kind of 
compression of DNS messages.

Here is the rough collection of ideas I presented during:

- Omit authority and additional sections in DNS responses
- Question section always size 1: omit QDCount field
- Make class and type optional (imply IN/AAAA)
- Self-delimiting numeric values for classes, types, counts, TTLs, etc.?
- Question section optional in responses?

I also briefly discussed two options:
- Put everything in a CBOR-array: Question section CBOR-array and answer 
section: CBOR-array of arrays, or
- implement some “remote getaddrbyname()” (i.e., query name (maybe 
type?), expect address as response)?

Carsten also proposed some way to squeeze some bytes out of the name, 
perhaps he could also write something up here on this.

We also thought about, but I did not explicitly mention, some 6LoWPAN- 
or SCHC-like address prefix compression, but that might need some 
additional architecture.

And then there is the question if this is even something we should 
discuss in the same draft as DoC itself and if this is even a core topic 
or rather should go to dnsop.

Cheers,
Martine

[1] https://datatracker.ietf.org/doc/draft-lenders-dns-over-coap/
[2] 
https://datatracker.ietf.org/meeting/113/materials/slides-113-core-dns-queries-over-coap-doc-00