snoop:

snoop behaves much in the same way as tcpdump in that it monitors network traffic for selected packet types and allows the user to extract desired information
from their data. The main distinction of snoop is the extent of the packet data that the user can examine, and an enhanced ``verbose'' mode that parses header
information to provide extensive information on packet structure. snoop can display the complete contents of the packet and can display underlying RPC, UDP,
and, IP frame information if desired. This makes snoop more useful than tcpdump in interpreting NFS transactions. However, file by file information is not compiled
by snoop since it operates independently upon each packet. snoop is designed as a system administrator maintenance command