Re: [core] RFC 7252 - 8.2 - Multicast - Request / Response Layer, page 67, top

[Achim Kraus <[e-mail]>]

Hi Jim,

thanks for the fast answer!

 > The unicast responder does not need to be on the default COAP port
number.

It's more the destination port of the request than the default CoAP port.

 > This would be especially true if you had two different server running
 > on the same piece of hardware. I find this to be very common for me in
 > testing because I am running 10 different CoAP servers on my laptop
 > and while they can share the multicast addresses, they need to end up
 > on different unicast ports.

OK, I see. Interesting. Using  different ports for multicast and unicast
makes it also easier to distinguish multicast from unicast.

(On the other side, it kills somehow the idea of a "service, bound to a
port" and it makes tracking the traffic with wireshark harder :-).
I will see, when I can spend some time into adjust the server-side
according this idea in your answer.)

best regards
Achim


Am 27.03.20 um 17:14 schrieb Jim Schaad:
>
>
> -----Original Message-----
> From: core <[e-mail]> On Behalf Of Achim Kraus
> Sent: Thursday, March 26, 2020 11:39 PM
> To: [e-mail]
> Subject: [core] RFC 7252 - 8.2 - Multicast - Request / Response Layer, page
> 67, top
>
> Hi list,
>
> RFC 7252 - 8.2 - Multicast - Request / Response Layer, page 67, top
>
> "When matching a response to a multicast request, only the token MUST match;
> the source endpoint of the response does not need to (and will
> not) be the same as the destination endpoint of the original request."
>
> (4.1. Messages and Endpoint, "With no security, the endpoint is solely
> identified by an IP address and a UDP port number")
>
> Though it is obvious, that the IP address part is changing (from multicast
> destination to a unicast source), I 'm not sure, why the port should be
> considered to change as well.
>
>
> example:
> 192.168.1.50:15683 -> 224.0.1.187:5683   (multicast request)
>
> 192.168.1.50:15683 <- 192.168.1.40:5683  (unicast response, I would expect)
>
> 192.168.1.50:15683 <- 192.168.1.40:7843  (unicast response, the spec.
> also allows)
>
> So,
>
> - was a change of the port (2. example response) considered when writting
> that definition?
> - if yes, what was the reason to do so?
>
> [JLS] My response would be that the answer is yes.  The unicast responder
> does not need to be on the default COAP port number.  This would be
> especially true if you had two different server running on the same piece of
> hardware.   I find this to be very common for me in testing because I am
> running 10 different CoAP servers on my laptop and while they can share the
> multicast addresses, they need to end up on different unicast ports.
>
> Jim Schaad
>
>
> best regards
> Achim Kraus
>
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