OPC UA Multicast Discovery

Question

519 views Asked by Rakshan Premsagar Kapikad At 10 December 2020 at 10:05

I am a beginner in OPC UA, exploring the discovery mechanisms mentioned in part 12 of the specification. I have a couple of queries.

In the Multicast extension discovery, the server registers to its Local discovery server(LDS ME), and when client does the registration to its LDS-ME, the client side LDS-ME issues a multicast probe for which the server side LDS-ME responds with an announcement, thus allowing the client to know the list of servers in the network. My question here is, why is the process referred as Multicast probe and multicast announcement. Because as per the mDNS specification, probe and announcement are used initially to secure unique ownership of a resource record. Anybody could tell me why is it referred as probe and announce?
In the open62541 stack, with the discovery examples, running the server_lds.c, i get a log message saying "Multicast DNS: outbound interface 0.0.0.0, it means that the first OS interface is used (you can explicitly set the interface by using 'discovery.mdnsInterfaceIP' config parameter)". Now theory says multicast dns IP should be 224.0.0.251: 5353 Why is it being set to 0.0.0.0? Could anyone please let me know?

Regards, Rakshan

There are 1 answers

**twooBeers** · Answer 1 · 2020-12-18 11:18:32

There is no relation to the words "probe" and "announce" used in the mDNS Spec. It just says probe, means look-up or query, and announce like "there are the follwing results related to your probe request".
0.0.0.0 means here every Ipv4 interface is used (bound). So every capable interface in your system will be configured for mDNS. Should be the way you mentioned.