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

[Klaus Hartke <[e-mail]>]

Esko Dijk wrote:
> However CoAP does define that a Server responds from the same endpoint that received the request, I believe. See below text quotes and analysis.

Yes. In the simple CoAP-over-UDP unicast NoSec case, if a request
message is sent from an endpoint 192.168.0.1:54321 ("client") to an
endpoint 192.168.0.100:5683 ("server"), the response message must be
sent from the endpoint 192.168.0.100:5683 to the endpoint
192.168.0.1:54321.

The response message cannot be sent from any other endpoint, because
then the client couldn't match the incoming message to its pending
request (it would appear to come from a different server). The
response message also cannot be sent to any other endpoint, because
then the client wouldn't get the message (it would be sent to a
different client).

I view multicast messages basically like e-mail mailing lists. E.g.
(IMO): A request message is sent from the endpoint 192.168.0.1:54321
to the special endpoint 224.0.1.187:9999, the message magically shows
up as incoming message at the endpoint 192.168.0.100:5683, and the
response message must be sent from the endpoint 192.168.0.100:5683 to
the endpoint 192.168.0.1:54321.

Klaus