Bit,Description,Reference
0,IS-IS Up/Down Bit (D-bit),[RFC9552]
1,"OSPF ""no unicast"" Bit (N-bit)",[RFC9552]
2,"OSPF ""local address"" Bit (L-bit)",[RFC9552]
3,"OSPF ""propagate NSSA"" Bit (P-bit)",[RFC9552]
4-7,Unassigned,