Some named pipes are used as MSRPC endpoints, i.e, they are used to carry DCE RPC PDU (Protocol Data Units). Compared to other RPC transports, the ncacn_np transport is different because it usually does not involve authentication at the DCE RPC level. Instead, authentication information is obtained from the SMB session established priorly.
However, it is possible to have unauthenticated DCE RPC sessions using SMB NULL sessions. In that case, there is no authentication, neither at the SMB level nor at the DCE RPC level.
Also, contrary to RPC services listening on ncacn_ip_tcp or ncadg_ip_udp, the portmapper service is generally not necessary for RPC services using named pipes, as the named pipe name usually identifies the RPC interface.