Re: [core] coap discovery

Michael Richardson <> Wed, 18 August 2021 01:48 UTC

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From: Michael Richardson <>
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Date: Tue, 17 Aug 2021 21:47:50 -0400
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Subject: Re: [core] coap discovery
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Christian Amsüss <> wrote:
    >> The "CBORUDP" provides for a stateless (i.e. stored in the network)
    >> record of where the packets come from.

    > So a bit like HTTP's CONNECT, and because there's CoAP as a transport
    > and since 8974 it has extended tokens, it can be stateless. Got it.
    > (Will this be specified for standalone use? I don't know to think of it
    > yet, but it's definitely intriguing).

It's not like HTTP CONNECT.
It's a reverse proxy.  The destination is forced by the proxy.
In order to remove the memory state of the proxy, we store in the network.
For (EDHOC)/PSK-OSCORE over CoAP, the proxy can mess with CoAP options.
But, DTLS keeps us from doing that.

    > If I've formed the right mental model here, there's two things that the
    > proxy can discover on the register (where 2001:db8:1:: might be the
    > actual network, and 2001:db8:2:: the network that's inside the UDP
    > tunnels -- may be the same addresses but may be not):

Just to clarify, there is no IP header inside the tunnel.

    > * The endpoint of the CoAP UDP service:
    > <coap://[2001:db8:1::1]/udp>;rt=cborudp (or ;rt=brski-yyy)


    > If so, and if the analogy from 9031 holds, then what the proxy needs to
    > discover is the /udp endpoint.

    > To that endpoint, it does talk CoAP, so
    > it's perfectly legitimate to discover it as a CoAP resource. Of the
    > inside traffic, or its relation to the outside resource, no statement
    > even needs to be discovered.

No, that's not the case.  To the proxy, it speaks "cborudp".

Michael Richardson <>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide