There are a number of miscellaneous files relating to network configuration under linux that might be of interest. You may never have to modify these files, but it is worth describing them so you know what they contain and why they are used.
The /etc/protocols file is a database that maps protocol id numbers against protocol names. This is used by programmers to allow them to specify protocols by name in their programs. The file is also used by some programs such as tcpdump to allow them to display names instead of numbers in their output. The general syntax of the file is:
protocolname number aliases
The /etc/protocols file supplied with the Debian distribution is as follows:
# /etc/protocols: # $Id: Net-HOWTO.sgml,v 220.127.116.11 2001/01/17 19:55:16 lx Exp $ # # Internet (IP) protocols # # from: @(#)protocols 5.1 (Berkeley) 4/17/89 # # Updated for NetBSD based on RFC 1340, Assigned Numbers (July 1992). ip 0 IP # Internet protocol, pseudo protocol number icmp 1 ICMP # Internet control message protocol igmp 2 IGMP # Internet Group Management ggp 3 GGP # gateway-gateway protocol ipencap 4 IP-ENCAP # IP encapsulated in IP (officially ``IP'') st 5 ST # ST datagram mode tcp 6 TCP # transmission control protocol egp 8 EGP # exterior gateway protocol pup 12 PUP # PARC universal packet protocol udp 17 UDP # user datagram protocol hmp 20 HMP # host monitoring protocol xns-idp 22 XNS-IDP # Xerox NS IDP rdp 27 RDP # "reliable datagram" protocol iso-tp4 29 ISO-TP4 # ISO Transport Protocol class 4 xtp 36 XTP # Xpress Tranfer Protocol ddp 37 DDP # Datagram Delivery Protocol idpr-cmtp 39 IDPR-CMTP # IDPR Control MessTransfernsport rspf 73 RSPF # Radio Shortest Path First. vmtp 81 VMTP # Versatile Message Transport ospf 89 OSPFIGP # Open Shortest Path First IGP ipip 94 IPIP # Yet Another IP encapsulation encap 98 ENCAP # Yet Another IP encapsulation
The /etc/networks file has a similar function to that of the /etc/hosts file.This file provides a simple database of network names against network addresses. Its format differs in that there may be only two fields per line, and that the fields are coded as:
An example might look like:
loopnet 127.0.0.0 localnet 192.168.0.0 amprnet 18.104.22.168
You will get a display of the network name (NOT its address) while using a command like route in the following instance: the destination is a network, and that network has an entry in the /etc/networks file.