There appears to be some sort of problem with the way SO and RockNSM set parameters for their monitoring interfaces, at least as far as they interact with VirtualBox 6.0.4 on Ubuntu 18.04. My workaround will hopefully hold for now, but I need to take a closer look at the NIC options because I may have introduced another fault. The moral of the story is that I should have immediately checked after installation that both SO and RNSM were seeing both sides of the traffic I expected them to see.”]
Source: https://taosecurity.blogspot.com/2019/04/troubleshooting-nsm-virtualization.html