Protocol.ora

Starting with Oracle 9i, the protocol.ora file is no longer being used. All (or, most?) protocol.ora parameters were moved to the sqlnet.ora file. These parameters enable you to configure database access and TCP/IP related settings. They include:

TCP.NODELAY 
TCP.EXCLUDED_NODES 
TCP.INVITED_NODES 
TCP.VALIDNODE_CHECKING 

This file was located in $ORACLE HOME/network/admin on UNIX systems, and in ORACLE HOME\network\admin on Windows.

Oracle's Net Manager (netmgr), when first started, will automatically move protocol.ora parameters into your sqlnet.ora file.