IPv6 Filtering: Secured

The RAX120 (and presumably other RAX-class routers) sets the “IPv6 Filtering” option to “Secured” by default (see ADVANCED | Advanced Setup | IPv6). The only information provided about this firewall setting in the User Manual is that “the router inspects both TCP and UDP packets” when it is enabled.

What specifically is "IPv6 Filtering" doing?  Insights from the forum community will be most appreciated.