Re: [core] [Anima] constrained resources at root for debugging connectivity

Carsten Bormann <> Thu, 22 July 2021 08:43 UTC

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From: Carsten Bormann <>
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Date: Thu, 22 Jul 2021 10:43:32 +0200
Cc: Esko Dijk <>, "" <>, "" <>
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To: Michael Richardson <>
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Subject: Re: [core] [Anima] constrained resources at root for debugging connectivity
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> On 2021-07-21, at 21:36, Michael Richardson <> wrote:
> Signed PGP part
> Esko Dijk <> wrote:
>> There is already a "CoAP ping" described in RFC 7252 that can be
>> used. It does not access any resource, just the CoAP server endpoint at
>> CoAP message layer. As a side effect of this ping your DTLS stack will
>> set up the connection which is handy.
> I recalled that later in the day that CoAP "ping" is not connected to CoAP
> "echo" :-)

The Echo option is not an echo in the sense of an ICMP echo.
(Maybe we should fix the name to “cookie”.)

> I think that there is also potentially a need for a way to debug possible MTU
> issues.

Good point, CoAP Ping (empty CON messages) cannot do that.

Actually, the fact that it was possible to set up DTLS should give one considerable confidence; the CoAP Ping is not needed to verify pure presence.  Verifying that that server actually speaks a specific protocol would need to be part of that protocol though.

Also, cough, cough, gives you a nice way to ping a DTLS server with different MTU sizes.
(Ignoring the fact that an incorrect implementation led to the biggest TLS, er, “event” we ever had.)

Grüße, Carsten