SVR4 supports the Data Link Provider Interface (DLPI) which is a streams implementation of the OSI Data Link Service Definition. Most versions of SVR4 still support version 1 of the DLPI, SVR4.2 supports both versions 1 and 2, and Sun's Solaris 2.x supports version 2, with additional enhancements.
Network monitoring programs such as tcpdump must use the DLPI for raw access to the data-link device drivers. In Solaris 2.x the packet filter streams module has been renamed pfmod and the buffer module has been renamed bufmod.
Although Solaris 2.x is still new, an implementation of tcpdump should appear someday. Sun also supplies a program named snoop that performs functions similar to tcpdump. ( snoop replaces the SunOS 4.x program named etherfind. ) The author is not aware of any port of tcpdump to vanilla SVR4.