pfSense » pfSense Packages

The directive is not set in vtysh because the nssa directive is not recognized. Only normal areas and stub areas seem to be available. Below is for 2.4.4.

pfSense2.sptest.net.local(config-ospf6)# area 0.0.4.175 nssa
% Unknown command: area 0.0.4.175 nssa
pfSense2.sptest.net.local(config-ospf6)# area 0.0.4.175
export-list Set the filter for networks announced to other areas
filter-list Filter networks between OSPF6 areas
import-list Set the filter for networks from other areas announced to the specified one
range Configured address range
stub Configure OSPF6 area as stub
pfSense2.sptest.net.local(config-ospf6)# area 0.0.4.175

Side note:
Our most common use case for using a product like pfSense is as a North-South Firewall. In that case nssa is the typical area type.
Because we are talking about OSPFv3/IPv6, a normal area would be an option as well (the amount of IPv6 routes in our environment is a lot smaller than the number of IPv4 routes)

Update:
It doesn't seem like FRR supports the NSSA area type. In fact, according to the documentation, it looks like it only really supports the Normal area type.
As a result, I would update the UI and "cleanup" Disable FIB updates. In addition, I'd suggest to rename this field to "Area type" with Normal (default) being the only option at this time (unless stub has been proven to be a valid option with the latest FRR release).