#

# The loopback network is used only for intra-machine communication

#

loopback     127

#

# Internet networks

#

arpanet         10                arpa     # Historical

subnet          190.109.252

subnet-seg1     190.109.252.32

subnet-seg2     190.109.252.64</PRE>

<H4 ALIGN="CENTER">

<CENTER><A ID="I38" NAME="I38">

<FONT SIZE=3><B>Choosing the Netmask for a Network&#151;</B><B><I>/etc/netmasks</I></B>

<BR></FONT></A></CENTER></H4>

<P>Normally when a netmask is needed, the IP system looks at the address class and chooses a netmask that matches the class of the address. However, as in the subnetting example, often a different netmask is needed. These exceptions to the rule are listed 

in the netmasks file as shown in this example:

<BR></P>

<PRE>#

# The netmasks file associates Internet Protocol (IP) address

# masks with IP network numbers.

# 

#      network-number     netmask

#

# Both the network-number and the netmasks are specified in

# &quot;decimal dot&quot; notation, e.g:

#

#                              128.32.0.0 255.255.255.0

#

190.109.252.0      255.255.255.0

190.109.252.32     255.255.255.224

190.109.252.64     255.255.255.224</PRE>

<P>A command that needs a netmask can either take the netmask as an override on the command line or consult the netmasks file to determine if there is a specific netmask before resorting to calculating one based on the class of the address.

<BR></P>

<H4 ALIGN="CENTER">

<CENTER><A ID="I39" NAME="I39">

<FONT SIZE=3><B>Mapping Names to Machines&#151;</B><B><I>/etc/ethers</I></B>

<BR></FONT></A></CENTER></H4>

<P>BOOTP and RARP need a file to map EtherNet addresses into IP numbers. This is provided by the ethers file, which maps the EtherNet MAC address into a hostname. Then the hosts file is used to map this into an IP address.

<BR></P>

<PRE>#

# The ethers file associates ethernet addresses with hostnames

#

08:00:20:0e:b9:d3      gateway

08:00:20:11:30:d0      sn1-router

08:00:20:0e:1d:0b      sn1-gateway

08:00:20:0b:de:0d      sn1-host</PRE>

<P>By placing the IP address in only the hosts file and making use of RARP for assigning network numbers, it is possible to readdress an entire network just by changing the hosts file and rebooting the machines. This makes changes very convenient.

<BR></P>

<H4 ALIGN="CENTER">

<CENTER><A ID="I40" NAME="I40">

<FONT SIZE=3><B>Mapping Names to Interfaces&#151;</B><B><I>/etc/hostname.</I></B><B>??n</B>

<BR></FONT></A></CENTER></H4>

<P>Many UNIX systems have more than one network interface. Each network interface on a host has its own IP address. Because a node name can appear only once in the /etc/hosts file, each interface also has its own node name. So the node, on boot, still 
needs to know which name, and therefore which IP address, to use on which network interface.

<BR></P>

<P>This is provided by the file /etc/hostname.<I>??n</I> where <I>??</I> is the name of the interface type, and <I>n</I> is a digit referring to the interface number. On Suns this is usually /etc/hostname.le0 for the first interface, /etc/hostname.le1 for 

the second, and so on.

<BR></P>

<P>This file contains just one line with one word on that line, the hostname to use for that particular interface:

<BR></P>

<PRE>fasthost</PRE>

<H5 ALIGN="CENTER">

<CENTER><A ID="I41" NAME="I41">

<FONT SIZE=3><B>Naming Supported Protocols&#151;</B><B><I>/etc/protocols</I></B>

<BR></FONT></A></CENTER></H5>

<P>To enable the diagnostic output of the utilities to list the protocols by name rather than by protocol number, a mapping is kept in the file /etc/protocols. This file is provided by the vendor and should not need changing. Not all the protocols listed 
in this file are necessarily supported on your system. An example of the contents of /etc/protocols is as follows:

<BR></P>

<PRE>#

# Internet (IP) protocols

#

ip        0      IP        # internet protocol, pseudo protocol number

icmp      1      ICMP      # internet control message protocol

ggp       3      GGP       # gateway-gateway protocol

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       # &quot;reliable datagram&quot; protocol</PRE>

<H5 ALIGN="CENTER">

<CENTER><A ID="I42" NAME="I42">

<FONT SIZE=3><B>Naming Supported Services&#151;</B><B><I>/etc/services</I></B>

<BR></FONT></A></CENTER></H5>

<P>Programs that wish to connect to a specific port use the services file to map the service name to the port number. This file is shipped from your vendor with all the default services in it. Local services can be added to support databases or any local 
extensions desired. The file is large, so the following example is only a small extract. Remember that ports smaller than 1024 are privileged and can only be listened on by processes owned by root.

<BR></P>

<PRE>#

# Network services, Internet style

# This file is never consulted when the NIS are running

#

tcpmux      1/tcp                    # rfc-1078

echo        7/tcp

echo        7/udp

discard     9/tcp      sink null

discard     9/udp      sink null

systat      11/tcp     users

daytime     13/tcp

daytime     13/udp

netstat     15/tcp

chargen     19/tcp     ttytst source

chargen     19/udp     ttytst source

ftp-data    20/tcp

ftp         21/tcp

telnet      23/tcp

smtp        25/tcp     mail

time        37/tcp     timserver

time        37/udp     timserver

name        42/udp     nameserver

whois       43/tcp     nicname          # usually to sri-nic

domain      53/udp

domain      53/tcp

hostnames   101/tcp    hostname         # usually to sri-nic

sunrpc      111/udp

sunrpc      111/tcp

ident       113/tcp    auth tap

#

# Host specific functions

#

bootps      67/udp                      # bootp server

bootpc      68/udp                      # bootp client

tftp        69/udp

rje         77/tcp

finger      79/tcp

link        87/tcp     ttylink

supdup      95/tcp

iso-tsap    102/tcp

x400        103/tcp                     # ISO Mail

x400-snd    104/tcp

csnet-ns    105/tcp

pop-2       109/tcp                     # Post Office

auth        113/tcp

uucp-path   117/tcp

nntp        119/tcp    usenet           # Network News Transfer

ntp         123/tcp                     # Network Time Protocol

ntp         123/udp                     # Network Time Protocol

snmp        161/udp

#

# UNIX specific services

#

# these are NOT officially assigned

#

exec        512/tcp

login       513/tcp

shell       514/tcp    cmd              # no passwords used

printer     515/tcp    spooler          # line printer spooler

courier     530/tcp    rpc              # experimental

uucp        540/tcp    uucpd            # uucp daemon

biff        512/udp    comsat

who         513/udp    whod

syslog      514/udp

talk        517/udp

ntalk       518/udp

route       520/udp    router routed

timed       525/udp    timeserver

new-rwho    550/udp    new-who          # experimental

rmonitor    560/udp    rmonitord        # experimental

monitor     561/udp                     # experimental

pcserver    600/tcp                     # ECD Integrated PC board srvr

kerberos    750/udp    kdc              # Kerberos key server

kerberos    750/tcp    kdc              # Kerberos key server</PRE>

<P>The format of the file is the name of the service followed by white space, then the port number, followed by a / and the protocol (either TCP or UDP). This is optionally followed by nicknames for the service. If a service is available both under UDP and 

TCP it must be listed twice in the file, once for UDP and once for TCP.

<BR></P>

<H5 ALIGN="CENTER">

<CENTER><A ID="I43" NAME="I43">

<FONT SIZE=3><B>Binding Daemons to Services&#151;</B><B><I>/etc/inetd.conf</I></B>

<BR></FONT></A></CENTER></H5>

<P>Rather than having each task listen for connections on its own ports, UNIX uses a common daemon to listen on many ports at once. This is the Internet services daemon or inetd. It listens on every port listed in its configuration file. When it receives a 

connection it forks off and starts the appropriate service daemon. Some services are handled internally by inetd, including daytime and echo.

<BR></P>

<P>When you change the inetd.conf file you need to signal the daemon to reread the file. Sending inetd the HUP signal causes it to reread the file. HUP is the signal 1 so you can use the following commands to have inetd reread the /etc/inetd.conf file:

<BR></P>

<PRE>kill -HUP <I>pid</I></PRE>

<P>Alternatively, you can enter this:

<BR></P>

<PRE>kill -1 <I>pid</I></PRE>

<P>In these commands <I>pid</I> is replaced by the <I>pid</I> of the inetd process, which will cause inetd to reread its configuration file. The following is a small sample of the file to show the format:

<BR></P>

<PRE>#

# Configuration file for inetd(1M).  See inetd.conf(4).

#

# To re-configure the running inetd process, edit this file, then

# send the inetd process a SIGHUP.

#

# Syntax for socket-based Internet services:

#  &lt;service_name&gt; &lt;socket_type&gt; &lt;proto&gt; &lt;flags&gt; &lt;user&gt; &lt;server_pathname&gt; &lt;args&gt;

#

# Syntax for TLI-based Internet services:

#

#  &lt;service_name&gt; tli &lt;proto&gt; &lt;flags&gt; &lt;user&gt; &lt;server_pathname&gt; &lt;args&gt;

#

# Ftp and telnet are standard Internet services.

#

ftp       stream     tcp     nowait     root     /etc/in.tcpd     in.ftpd

telnet    stream     tcp     nowait     root     /etc/in.tcpd     in.telnetd

#

# Shell, login, exec, comsat and talk are BSD protocols.

#

shell     stream     tcp     nowait     root     /etc/in.tcpd     in.rshd

login     stream     tcp     nowait     root     /etc/in.tcpd     in.rlogind

#

#

# RPC services syntax:

#  &lt;rpc_prog&gt;/&lt;vers&gt; &lt;endpoint-type&gt; rpc/&lt;proto&gt; &lt;flags&gt; &lt;user&gt; \

#  &lt;pathname&gt; &lt;args&gt;

#

# &lt;endpoint-type&gt; can be either &quot;tli&quot; or &quot;stream&quot; or &quot;dgram&quot;.

# For &quot;stream&quot; and &quot;dgram&quot; assume that the endpoint is a socket descriptor.

# &lt;proto&gt; can be either a nettype or a netid or a &quot;*&quot;. The value is

# first treated as a nettype. If it is not a valid nettype then it is

# treated as a netid. The &quot;*&quot; is a short-hand way of saying all the

# transports supported by this system, ie. it equates to the &quot;visible&quot;

# nettype. The syntax for &lt;proto&gt; is:

#     *|&lt;nettype|netid&gt;|&lt;nettype|netid&gt;{[,&lt;nettype|netid&gt;]}

# For example: 

# dummy/1   tli   rpc/circuit_v,udp   wait   root   /tmp/test_svc   test_svc

#

# System and network administration class agent server

#

# This is referenced by number because the admind agent is needed for the

# initial installation of the system. However, on some preinstalled systems

# the SNAG packages may not be present. Referencing the service by number

# prevents error messages in this case.

#

100087/10     tli     rpc/udp     wait     root     /usr/sbin/admind     admind</PRE>

<H5 ALIGN="CENTER">

<CENTER><A ID="I44" NAME="I44">

<FONT SIZE=3><B