5.9. Other miscellaneous network related configuration files.

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.

5.9.1. /etc/protocols

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 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

5.9.2. /etc/networks

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:

  networkname networkaddress

An example might look like:


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.