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Post by rakshan »

Hello there,
Posting a query on LDS ME for more clarity and Understanding.
For the multicast subnet discovery, part 12 says it is useful when clients do not have an idea about the servers present on the network.
In that scenario, the server registers to the LDS-ME using registerServer2 service. Next, when client pluggs itself in, the LDS-ME of the client issues a probe message on which the LDS-ME of the server responds with an announcement providing the list of ServerURL's.

Having read the mDNS specification, I do not seem to get a clarity as to why is it referred as probing here. Probing ,in mDNS terms is used to have a single authority over the various Resource records of a domain. Could you please tell me how is it probing here in OPC UA?
Also announcment somehow makes sensse, as to making the registered server available for discovery.

Below, i have summarised my understanding. Please correct me if I am wrong..
Looking into the Annexure(part 12), I see that mDNS uses the DNS SRV type query to check for the servers available, so the probe message will be (Qtype = SRV, Qclass =IN, Qname=, and in response it gets an announcement with the host and port information too, example of which is given as " 86400 IN SRV 0 5 4840" in part 12, which ultimately gets mapped to the discoveryURL.

Does the mapping to URL happen in the findServersinNetwork method?
When does the mapping happen?

Extremely curious. Apologies is this is really basic. Please let me know


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