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Linux man pages : protocols (5)
PROTOCOLS(5)		   Linux Programmer's Manual		  PROTOCOLS(5)


protocols - the protocols definition file


This file is a plain ASCII file, describing the various DARPA internet protocols that are available from the TCP/IP subsystem. It should be consulted instead of using the numbers in the ARPA include files, or, even worse, just guessing them. These numbers will occur in the proto- col field of any ip header. Keep this file untouched since changes would result in incorrect ip packages. Protocol numbers and names are specified by the DDN Network Information Center. Each line is of the following format: protocol number aliases ... where the fields are delimited by spaces or tabs. Empty lines are ignored. If a line contains a hash mark (#), the hash mark and the part of the line following it are ignored. The field descriptions are: protocol the native name for the protocol. For example ip, tcp, or udp. number the official number for this protocol as it will appear within the ip header. aliases optional aliases for the protocol. This file might be distributed over a network using a networkwide nam- ing service like Yellow Pages/NIS or BIND/Hesiod.


/etc/protocols The protocols definition file.


getprotoent(3) Guide to Yellow Pages Service Guide to BIND/Hesiod Service Linux 1995-10-18 PROTOCOLS(5)