The underlying cause looks to be https://github.com/dotnet/runtime/issues/28630.
Basically, it's an access denied bug.
It looks like multicasts need the same access rights as broadcasts on some systems.
Fixing this required the removal of the code that attempted to detect virtual interfaces. Not wanting to remove functionality, but not able to keep the code in place, I implemented a work around solution (see 4 below).
Whilst in the area, I also fixed a few minor bugs i encountered (1, 5, 6 below) and stopped SSDP messages from going out on non-LAN interfaces (3)
All these changes are related.
Changes
1 IsInPrivateAddressSpace - improved subnet code checking
2 interfaces with no gateway were being excluded from SSDP blasts
3 filtered SSDP blasts from not LAN addresses as defined on the network page.
4 removed #986 mod - as this was part of the issue of #2986. Interfaces can be excluded from the LAN by putting the LAN address in brackets. eg. [10.1.1.1] will exclude an interface with ip address 10.1.1.1 from SSDP
5 fixed a problem where an invalid LAN address causing the SSDP to crash
6 corrected local link filter (FilterIPAddress) to filter on 169.254. addresses
Fixing this required the removal of the code that attempted to detect virtual interfaces. Not wanting to remove functionality, but not able to keep the code in place, I implemented a work around solution (see 4 below).
Whilst in the area, I also fixed a few minor bugs i encountered (1, 5, 6 below) and stopped SSDP messages from going out on non-LAN interfaces (3)
All these changes are related.
Changes
1 IsInPrivateAddressSpace - improved subnet code checking
2 interfaces with no gateway were being excluded from SSDP blasts
3 filtered SSDP blasts from not LAN addresses as defined on the network page.
4 removed #986 mod - as this was part of the issue of #2986. Interfaces can be excluded from the LAN by putting the LAN address in brackets. eg. [10.1.1.1] will exclude an interface with ip address 10.1.1.1 from SSDP
5 fixed a problem where an invalid LAN address causing the SSDP to crash
6 corrected local link filter (FilterIPAddress) to filter on 169.254. addresses
