Resolution:
Description:
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1). On the VMS system,  have 2 tibrvlisten on box A
tibrvlisten -network ";239.255.17.178" -service 7744
tibrvlisten -network ";239.155.17.188" -service 7745

2). Run tibrvsend -network ";239.255.17.178" -service 7745

You will notice:

A).  Despite the fact that specifications don't match either client on A one of the clients receives the data, and B).  It will be the client on the same group as the data was published.

The multcast behavior you noticed is OS behavior. We noticed with mctst.
CR RV-2884 (which is for Linux)– whereby Linux delivers all Multicast data to all UDP ports , which is address in RV 8.4.0 HF5.
Unfortunately the solution that was done for Linux is Linux specific and is not applicable to OpenVMS


Resolution:
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You can avoid the problem by not using the same multicast group across different services.