A text file that provides resolution of protocol names into their respective RFC-defined protocol numbers on a TCP/IP network. The entries in the protocol file are friendly names for TCP/IP protocol numbers and can be used for well-known service (WKS) records in Domain Name System (DNS) servers and other Windows Sockets applications.
The protocol file is in the following location on computers running Microsoft Windows:
Each line in the protocol file contains the standard name for a protocol followed by the assigned number as defined in Request for Comments (RFC) 1060, an alias, and an optional comment prefixed with a pound sign (#). The following example comes from the sample protocol file included with Windows 95 and Windows 98:
ip 0 IP # Internet protocol
icmp 1 ICMP # Internet control message protocol
ggp 3 GGP # Gateway-gateway protocol
tcp 6 TCP # Transmission control protocol