Re: [Ace] WGLC for draft-ietf-ace-coap-est

Michael Richardson <> Mon, 04 March 2019 21:55 UTC

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Date: Mon, 04 Mar 2019 16:55:16 -0500
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Subject: Re: [Ace] WGLC for draft-ietf-ace-coap-est
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Panos Kampanakis (pkampana) <> wrote:
    >> But can't the client just be configured out-of-band with the URIs directly?

    > That is right. We could mandate only .well-known URIs. But I think we
    > ought to let a deployment use non-default URIs. For example some
    > usecase might not want to send the .well-known in the URI to save
    > transmission bytes and thus use a custom short URI. If the URI change
    > takes place after deployment client will find that out with a
    > discovery. Similarly, a usecase might initially not support one of the
    > optional requests like server-side keygen. If the server adds support
    > sometime in the future, the client could find out using discovery. And
    > we ought to let the client be able to recover in case the well-known
    > request URI fails for some reason and he wants to see what is supported
    > by the server.That is why we thought it is still worth to keep the
    > .well-known URIs along with the discovery.

also, EST-COAP is a building block for draft-ietf-anima-constrained-voucher
(containing constrained BRSKI) so preconfiguration won't work.   While
constrained BRSKI can operate on .well-known the LDevID renewal might occur
with a different server, and so discovery might be worthwhile.

There are two reasons for doing the resource discovery:

1) to get a multicast response when looking for a registrar.
2) to get a shorter name to save some bytes.

I think that (2) contributes negatively to code-complexity, and so if not
for (1), I'd prefer to live on /.well-known only.  But, I don't object
to having shorter URLs available for those that want to spend the code.

Michael Richardson <>ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-