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Marc SchierandCopilot
aeeef5b420
# Description `UdpDatagramTransport` joined multicast groups on the resolved network interface: the connection address's `NetworkInterface`, the `PreferredNetworkInterface` option, or the first operational interface. It never set `IP_MULTICAST_IF` / `IPV6_MULTICAST_IF`, though, so multicast data and discovery announcements left through the operating system's default multicast route. On a computer with several network interfaces, a publisher configured for one network sent on another, and subscribers on the configured network missed the messages (OPC 10000-14 §7.3.2.2, `NetworkAddressDataType.NetworkInterface`). `ConfigureSocket` now sets the multicast send interface to the resolved interface for IPv4 and IPv6 sockets. That includes the separate socket that sends discovery announcements for loopback-bound connections. A failure is logged at Debug level, like the other socket options. **Behavior change:** without a configured interface, multicast now leaves through the first operational non-loopback interface, which is the interface subscribers join on, instead of the default multicast route. `docs/PubSub.md` and the XML docs of `PreferredNetworkInterface` and `UdpNetworkInterfaceResolver` describe this and recommend naming the interface on multi-homed computers. Tests (`UdpDatagramTransportMulticastInterfaceTests`): - The IPv4 and IPv6 egress options equal the resolved interface. Before the fix they were `0.0.0.0` and `0`. - A publisher and subscriber pinned to the loopback interface exchange a payload. A raw control sender tells a host without loopback multicast apart from a publisher that sends elsewhere. The test fails with the bug on Linux; Windows also delivers local copies sent on other interfaces, so there it only confirms the exchange. ### Validation | Command | Result | | --- | --- | | `dotnet test tests/Opc.Ua.PubSub.Udp.Tests -f net10.0 -p:CustomTestTarget=net10.0 --filter "FullyQualifiedName~UdpDatagramTransportMulticastInterfaceTests"`, with the fix temporarily disabled | IPv4 and IPv6 option tests failed (`Expected: <192.168.178.101> But was: <0.0.0.0>`, `Expected: 4 But was: 0`) | | The same tests from the Windows-built binaries in a Linux container (`mcr.microsoft.com/dotnet/sdk:10.0`, `dotnet test Opc.Ua.PubSub.Udp.Tests.dll`), fix disabled, 5 runs | 3 of 3 failed in every run, including the loopback exchange (the control sender arrived, the publisher's multicast did not) | | Same, with the fix, 5 runs | 3 of 3 passed in every run | | `dotnet test tests/Opc.Ua.PubSub.Udp.Tests -f net10.0 -p:CustomTestTarget=net10.0` | 237 passed (Windows, and the same binaries in the Linux container) | | `dotnet test tests/Opc.Ua.PubSub.Udp.Tests -f net48 -p:CustomTestTarget=net48` | 232 passed | | `dotnet test tests/Opc.Ua.PubSub.Tests -f net10.0 -p:CustomTestTarget=net10.0` | 1490 passed, 1 skipped | | `dotnet build src/Opc.Ua.PubSub.Udp -c Release` (net10.0, net9.0, net8.0, net48) | 0 warnings | | The docs/PubSub.md first exchange (unicast loopback), run verbatim, with #4710 applied | 11 DataSets; the unsecured-frame warning appears once, as documented | ## Related Issues - No tracking issue. Found while verifying the PubSub first-exchange documentation (follow-up to #4555). ## Checklist - [ ] I have signed the [CLA](https://opcfoundation.org/license/cla/ContributorLicenseAgreementv1.0.pdf) and read the [CONTRIBUTING](https://github.com/OPCFoundation/UA-.NETStandard/blob/master/CONTRIBUTING.md) doc. - [x] I have added tests that prove my fix is effective or that my feature works and increased code coverage. - [x] I have added all necessary documentation. - [x] I have verified that my changes do not introduce (new) build or analyzer warnings. - [ ] I ran **all** tests locally using the **UA.slnx** solution against at least .net **framework** and .net **10**, and all passed. - [ ] I fixed **all** failing and flaky tests in the CI pipelines and **all** CodeQL warnings. - [ ] I have addressed **all** PR feedback received. --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>