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Document:	ULTRIX-32 Guide to Networking
Order Number:	AA-ME97A-TE
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Pages:	60
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ULTRIX-32
Guide to
Networking

Order No. M-ME97A-TE

ULTRIX-32 Operating System, Version 3.0

Digital Equipment Corporation

The information in this document is subject to change without notice and should not be
construed as a commitment by Digital Equipment Corporation. Digital Equipment Corporation
assumes no responsibility for any errors that may appear in this document.
The software described in this document is furnished under a license and may be used or
copied only in accordance with the terms of such license.
No responsibility is assumed for the use or reliability of software on equipment that is not
supplied by DIGITAL or its affiliated companies.

The following are trademarks of Digital Equipment Corporation:
DEC
DECnet
DEC US
MASS BUS
MicroVAX

PDP

Q-bus
RT
ULTRIX
ULTRIX-11
ULTRIX-32
UNIBUS

VAX
VAXstation
VMS
VT
UL TRIX Worksystem Software
~amaama

UNIX is a registered trademark of AT&T in the USA and other countries.
IBM is a registered trademark of International Business Machines Corporation.
MICOM is a registered trademark of Micom System, Inc.
This manual was written and produced by the ULTRIX Documentation Group in Nashua, New
Hampshire.

Contents

About This Manual
Audience ........ .. .......... .. .. ...... .. ... .. ... ... .. .............. .. .............. ....... .. ....... . ............. .

vii

Organization ....... .......................... ...... ..... ........... .. ........... .................. ..............

vii

Related Documents ........................................................................................

viii

Conventions .....................................................................................................

viii

1 Overview of Local Area Networks
1.1 Local Area Networks ..............................................................................

1-1

1.1.1 Components and Uses ................................................................
1.1.2 Internet Addresses ......................................................................

1-1
1-2

1.1.2.1 The Common Internet Address Notation .............................
1.1.2.2 The Alternate Internet Address Notation ............................

1-3
1-4

1.1.3 Network Classes ..........................................................................

1-5

1.1.3.1 Determining a Network Class ................................................

1-6

1.1.4 Internet Broadcast Addresses ....................................................
1.1.5 Routing Decisions ........................................................................

1-7
1-8

1.1.5.1 A Simple Local Area Network Routing Exercise ................

1-8

1.1.6 Internet Networks .......................................................................

1-9

1.1.6.1 Setting Up a Gateway (Example)

........................................ 1-10

1.1.6.1.1 Edit the /etc/hosts File ........................................................ 1-12
1.1.6.1.2 Inform the System of the New Route .............................. 1-13

1.1.6.2 Updating the Internal Routing Tables .................................. 1-14
1.1.6.2.1 Edit the /etc/networks File .................................................. 1-15
1.1.6.2.2 Update the Routing Tables .................................................. 1-15
1.1.6.3 Using a Gateway ...................................................................... 1-16
1.2 Subnet Routing ....................................................................................... 1-16
1.2.1 Using Subnet Masks .................................................................. 1-17
1.2.1.1 Subnet Routing on a Class A Network (Example) ............ 1-19
1.2.1.2 Subnet Routing on a Class B Network (Example) ............ 1-20
1.2.1.3 Setting Up Subnetworks (Example) ..................................... 1-21
1.2.1.3.1 Edit the /etc/hosts File ........................................................ 1-22
1.2.1.3.2 Inform the System of the New Routes ............................ 1-23
1.3 Local Area Network Files ..................................................................... 1-24
1.3.1 The /etc/inetd.conf File ...............................................................
1.3.2 The /etc/protocols File ................................................................
1.3.3 The /etc/services File ..................................................................
1.3.4 The /etc/networks File ................................................................
1.3.5 The /etc/re and /etc/re.local Files ..............................................
1.3.6 The /etc/hosts File ......................................................................
1.3. 7 The /etc/hosts.equiv File .............................................................
1.3.8 The .rhosts File ...........................................................................
1.3.9 The /usr/hosts Directory .............................................................
1.3.10 The /usr/spool/mqueue Directory .............................................
1.3.11 The /usr/spool/rwho Directory ..................................................

1-25
1-25
1-26
1-26
1-26
1-27
1-28
1-28
1-29
1-29
1-30

1.4 Network Maintenance Commands ......................................................... 1-30

2 Setting Up a loca I Area Network
2.1 Adding Your System to an Existing Local Area Network

2-1

2.1.1 Prerequisite Information .............................................................

2-2

2.1.1.1 Run the netsetup Command ..................................................
2.1.1.2 Reboot System to Effect Changes ........................................

2-2
2-3

2.2 Setting Up a Local Area Network .......................................................

2-3

2.2.1 Prerequisite Information .............................................................

2-4

2.3 Setting Up an Internet Network with Gateways ...............................

2-4

2.3.1 Set Up a Local Area Network .................................................
2.3.2 Establish a Host as a Gateway ................................................

2-5

2.4 Setting Up a Local Area Network With Subnet Routing ................

2-5

2.4.1 Prerequisite Information .............................................................

2-6

2.5 Updating Your Local Area Network ....................................................

2-6

2-4

Index

Figures
1-1:

A Local Area Network ........................................................................

1-2

1-2:

Two Networks and Several Hosts ..................................................... 1-10

1-3:

Two Networks Connected by a Gateway Host (alto) .................... 1-11

1-4:

Interpreting a Class A Subnet Mask and Internet Address

1-20

1-5:

Interpreting a Class B Subnet Mask and Internet Address

1-21

1-6:

Subnetwork Configuration with Point-to-Point Links ...................... 1-22

Tables
1-1:

Network Number Ranges

1-4

1-2:

Internet Address Format

1-6

1-3:

Binary and Decimal Ranges for the Three Network Classes .......

1-6

1-4:

Host oboe's /etc/hosts File - Simple Configuration .......................

1-9

1-5:

Host alto's /etc/hosts File - Internet Configuration ...................... 1-11

1-6:

Host alto's Modified /etc/hosts File - Internet Configuration ...... 1-12

1-7:

Host alto's Internal Routing Table - Internet Configuration ....... 1-14

1-8:

Common Interface Names .................................................................. 1-14

1-9:

Host flute's Updated /etc/hosts File ................................................. 1-23

1-10:

Host flute's Updated Internal Routing Table ................................ 1-23

About This Manual

The objective of this guide is to provide introductory, setup, and
maintenance information for a Local Area Network (LAN) . This guide will
also assist you in developing local area network management procedures.
It presents guidelines from which you can develop specific procedures for
your site.

Audience
This guide is meant for the person responsible for maintaining networks on
an ULTRIX-32 operating system. This person is usually the system
manager, but could be a network manager or the system manager who is
also a user of a MicroVAX processor running the ULTRIX-32 operating
system. This guide assumes that the reader is familiar with the ULTRIX32 system commands, the system configuration, the naming conventions
and an editor, such as vi or ed. It also assumes the reader knows the
names and addresses of the other systems on the network, if a local area
network already exists.

Organization
This manual consists of two chapters and an index.

The chapters are:

Chapter 1: Introduction
This chapter introduces the local area network. It provides the
background information needed to, set up and run a local area network
on your system. It describes basic local area network concepts.
Chapter 2: Setting Up a Local Area Network
This chapter describes how to use the netsetup command to
automatically set up and update a local area network on your system.
A description of the manual procedure is included for those who want
to understand how local area networks operate and which files are
affected by the network.
Subnetwork routing is described and network management methods are
provided.

Related Documents
You should have available the related hardware documentation for your
system. You also should have the other documents in the ULTRIX-32
documentation set.

Conventions
The following conventions are used in this manual:
special

In text, each mention of a specific command, option,
partition, pathname, directory, or file is presented in this
type.

command(x)

In text, cross-references to the command documentation
include the section number in the reference manual where
the commands are documented. For example: See the
cat(1) command. This indicates that you can find the
material on the cat command in Section 1 of the reference
pages.

literal

In syntax descriptions, this type indicates terms that are
constant and must be typed just as they are presented.

italics

In syntax descriptions, this type indicates terms that are
variable.

[ ]

In syntax descriptions, square brackets indicate terms that
are optional.
In syntax descriptions, a horizontal ellipsis indicates that
the preceding item can be repeated one or more times.

fun ct i on

In function definitions, the function itself is shown in this
type. The function arguments are shown in italics.

UPPERCASE

The ULTRIX- 32 system differentiates between lowercase
and uppercase characters. Enter uppercase characters only
where specifically indicated by an example or a syntax line.

example

In examples, computer output text is printed in this type.

example

In examples, user input is printed in this bold type.

This is the default user prompt in multiuser mode.

This is the default superuser prompt.

>>>

This is the console subsystem prompt.

In examples, a vertical ellipsis indicates that not all of the
lines of the example are shown.
<KEYNAME > In examples, a word or abbreviation in angle brackets
indicates that you must press the named key on the
terminal keyboard.
<CTRL/x>

In examples, symbols like this indicate that you must hold
down the CTRL key while you type the key that follows
the slash. Use of this combination of keys may appear on
your terminal screen as the letter preceded by the
circumflex character. In some instances, it may not appear
at all.

Overview of Local Area Networks 1

This chapter provides an overview of local area networks and subnetworks
(subnet routing) . It also discusses the files related to local area networks
and provides information on how to maintain them.
Each of the topics discussed builds upon the principles of the previous
topics:
•

Overview of local area networks

•

Subnet routing

•

Local area network files

•

Network maintenance commands

1.1

Local Area Networks

You should understand how local area networks operate before you install
them on your system. The next seven sections discuss:
•

Components and uses

•

Internet addresses

•

Net work classes

•

Internet broadcast addresses

•

Routing decisions

•

Internet networks

•

Updating the internal routing tables

1.1.1

Components and Uses

A local area network (LAN) is a group of two or more computer systems
connected by a transmission medium such as an Ethernet cable. Each
computer system is connected to the transmission medium by a hardware
interface such as a DEUNA.
The systems connected to the network are usually in the same building or
cluster of buildings and are usually under the same system administration.
A local area network is useful for transferring data and sharing resources
across systems. Figure 1-1 illustrates a local area network with three

hosts connected to an Ethernet wire.

Host
oboe

Host
alto

Network

98
Host
violin
ZK-0035U-HC

Figure 1-1: A Local Area Network

Each local area network has a unique network number. Each computer
system connected to the network is called a host and has a unique number
identifying it. In Figure 1-1, the network number is 98. The combination
of the network number and the host number is called the Internet address.
The /etc/hosts file lists each of the hosts that your system recognizes,
including each host's Internet address and name, and any alias host names.
The /etc/networks file lists each of the networks that your system
recognizes, including their names, network numbers, and any aliases.
Data is transferred over a local area network in two ways:
•

A broadcast message

•

A direct message

Daemons on each host, such as rwhod, broadcast data on a regular basis.
Broadcast data is received by all the hosts on that network.
In general, data that is sent directly to a host is not received by any
other host on the network.
1.1.2

Internet Addresses

For a host to communicate with a remote host, it must know the remote
host's Internet address.
This section describes the Internet address and its parts. Because the
Internet address defines the network class, network classes are also
described briefly in this section, and in detail in the following section.
Each host has its own Internet address that uniquely identifies it from any
other host on the network. The Internet address is made up of two parts,
thP, TIP,twork n11mhPr

()1"

~rlrlrA\;l\;l

~nrl

thA hnC!t n11mha...

o .... rl

l-.n ...

+,,.+ .... 1 .... ~

32 bits (four bytes). The network part of the Internet address specifies
the network class (Class A, Class B, or Class C) as well as the network
address.
There are two types of notation for an Internet address. The more
common notation is four fields separated by periods. The alternate
notation expresses the entire host part of the Internet address as one field.
1.1.2.1 The Common Internet Address Notation - A 32-bit Internet
address is divided into two parts, the network and the host.

The network part of the address must be the same for all hosts connected
to the same network. No two networks can have the same network
number if they are connected in any way, for example, by a cable or
gateway. A gateway allows systems on one network to communicate with
systems on another network.
The host part of the address must be a number unique to that specific
network. No two hosts on the same network can have the same host
number.
Note
If you are planning to set up a local area network, it is wise to

obtain a registered Internet address, even if you do not intend to
connect your network to an outside one. Then, if you choose to
connect to another network in the future, such as the Arpanet,
you will not need to change all your Internet Protocol (IP)
addresses.
To obtain a registered IP address application, call the Network
Information Center at 800-235-3155 or 415-859-3695.
If you have access to the Arpanet, you can send mail to:

nic@sri-nic.arpa

The more common of the two methods for notating an Internet address
uses four fields to describe the 32 bits in this format:
fie ldl. fie ld2. fie ld3. fie ld4
Each field ranges from 0 to 255 decimal, for example, 98.0.2.65.
For a Class A network, the first (left-most) of the four fields specifies the
network number and class. The remaining three fields specify the host
number and subnet address, if subnetworks are being used. The first field

can be from 1 to 126, inclusive.
Note

By convention, 127 is reserved as the loopback address, which is
defined in the /etc/networks and /etc/hosts files.
For a Class B network, the first two fields specify the network number
and class, and the remaining two fields specify the host number and subnet
address, if subnetworks are being used. The first field can be from 128 to
191 and the second field can be from 1 to 254.
For a Class C network, the first three fields specify the network number
and class, and the remaining field specifies the host number. The first
field can be from 192 to 223, the second field can be from 0 to 255, and
the third field can be from 1 to 254. Table 1-1 shows the ranges of the
network numbers for the three network classes.

Table 1e1: Network Number Ranges
Class

Number

A
B
C

1 through 126
128.1 through 191.254
192.0.1 through 223.255.254

An example of an Internet address for a host named oboe on a Class A
network that does not have subnetworks is 98.65. The network part of
the address is 98, and the host part of the address is 65.
1.1.2.2 The Alternate Internet Address Notation - The alternate
Internet address notation conveys the same information as the common
method. It has two parts: the network and the host. The network part
is notated exactly as described in the previous section. However, the host
part is always made up of only one field, which consists of a decimal value
of the host fields described above. For example, the IP address of
72.0.5.4 on a Class A network can be expressed in alternate notation as
72.1284. The IP address of 128.45.2.8 on a Class B network can be
expressed in alternate notation as 128.45.520. See inet( 3n) in the
ULTRIX Reference Pages for a discussion of the Internet address.

Note that jf you have an IP address where the middle two fields are zero
on a Class A network, you can obtain the alternate notation by dropping
the two middle fields. For example, the IP address of 48.0.0.5 can be
expressed as 48.5.
Another example of an Internet address of a host on a Class A network is
98.0.10.65. This Internet address could also be notated as 98.2625. The
host part of the alternate notation ( 2625) is arrived at by the following
calculation:
(10

1.1.3

x 256) + 65 = 2625

Network Classes

There are three types of networks: Class A, Class B, and Class C. The
class type depends upon how the network is configured. To understand
how the dnferent classes are determined, view the Internet address as a
32-bit number that defines the class type, network number, and host
number. There are two fields in the 32-bit Internet address number:
network

host

The network field provides two kinds of information: the network class
and the network number. The high-order bits in the network number
designate the network class of the Internet address, such as Class A.
Class A networks are determined when the first high-order bit is 0, Class
B networks are determined when the first two high-order bits are 10.
Class C networks are determined when the first three high-order bits are
110.
The bits in the network field designate the network number, such as 98,
and the bits in the host field designate the number of the host, such as
65.
Table 1-2 shows how the bits of an Internet address are divided for each
of the three network classes. In Table 1-2, the first one, two, or three
bits of the network field, depending upon the network class, are also
interpreted as the class type. The total number of bits, regardless of the
network class, is 32. In the table, n represents one bit in the network
part of the address, and h represents one bit in the host part of the
address. Note that the information in Table 1-2 applies whether you use
the common or alternate notation.

Table 1-2: Internet Address Format
Class

Class-Type/Network

Host

A
B
C

O/nnnnnnn
10/nnnnnn nnnnnnnn
110/nnnnn nnnnnnnn nnnnnnnn

hhhhhhhh hhhhhhhh hhhhhhhh
hhhhhhhh hhhhhhhh
hhhhhhhh

For example, assume a host has an Internet address of 98.65. The ClassType and Network fields share the value 98, and the Host field uses all the
bits in the value 65.
The system translates the Internet address of 98.65 into binary notation,
the result of which is 01100010.01000001. This binary number can be
placed in the same format as shown in Table 1-2:
A

01100010 01000001

Because the first number in the Class-Type/Network field is 0, the Internet
address 98.65 is on a Class A network.
Another example is network 130. In binary notation, decimal 130 is
10000010. Because the first two numerals are 10, network 130 is a Class
B network (see Table 1-1).
1.1.3.1 Determining a Network Class - Table 1-3 shows the binary and
decimal number ranges for the first byte of the network address for each
of the three network classes.

Table 1-3: Binary and Decimal Ranges for the Three Network Classes
Class

Binary Range

Decimal Range

A
B

00000000-01111111
10000000-10111111
11000000-11011111

0-127
128-191
192-223

From Table 1-3, you can see that any network number with the first byte
in the decimal range 0 through 127 is a Class A network, and the network

number consists of one byte. Any network number with the first byte in
the range 128 through 191 is a Class B network, and the network number
consists of two bytes. Any network number with the first byte in the
range 192 through 223 is a Class C network, and the network number
consists of three bytes.
To determine which network class is best for a particular site, you need to
know the network environment, including how many hosts will be on the
network and how many networks there will be.
For sites with few networks but numerous hosts, a Class A network is
best suited, because it has 24 bits in the host part of its Internet address.
The 24 bits allow for the most host-number combinations. There are seven
usable bits in the network part of the Internet address, which leaves 126
usable network-number combinations. This takes into account the reserved
network numbers of 0 and 127.
The Class B network is between the Class A and Class C networks in
terms of how the bits are divided for the Internet address. The Class B
network is best when the number of networks is about equal to the
number of hosts. The 32 bits of the Internet address are evenly divided
between the network and host parts of the address.
The Class C network is ideal for sites with numerous networks but few
hosts. This is because the Class C network has 21 usable bits in the
network part of its Internet address. The 21 bits allow up to 16,777,216
network-number combinations. There are eight bits in the host part of the
Internet address, which leaves 254 possible host-number combinations. This
takes into account some host numbers that are reserved for special
purposes. For example, you cannot use all ones ( 1) or all zeros ( 0),
because these numbers are reserved for the broadcast address. See Section
1.1.4 for further information about Internet broadcast addresses.
Remember that each host number must be unique on its network.
The Class C network is ideal for sites with numerous point-to-point links.
A point-to-point link is one in which only two systems, one on each end of
the link, can be connected at one time. An Ethernet, on the other hand,
can be shared by numerous systems at any given time.
1.1.4

Internet Broadcast Addresses

An Internet broadcast address is the address used to send messages to all
the hosts on a network. For example, a program such as rwhod,
broadcasts information such as the list of users on a particular host.
Every other host on the network receives this information. The default
format of the Internet broadcast address consists of the network number
followed by all ones ( 1) . The network number includes the subset, if there
is one. "All ones" means all of the bits in the host field are set to one.

For example, a broadcast address for a host on a Class B network is:
129.39.255.255

Each host on a network must have the same Internet broadcast address.
It may be necessary to alter the Internet broadcast address to all zeros
( 0) for compatibility reasons. Some operating systems, such as 4.2BSD
and the ULTRIX-32 operating systems prior to Version 1.2, used all zeros
for their broadcast address. The industry standard default is all ones, and
the ULTRIX-32 operating system follows this standard.
Problems can occur when systems using all zeros coexist on the same
network as systems using all ones. If each system uses its default
broadcast address (one system has all zeros, the other has all ones), then
the two UNIX operating systems may not be able to interpret each other's
broadcast messages.
In this situation, you can use the ifconfig command to alter the Internet
broadcast address.
1.1.5

Routing Decisions

Data can be sent by numerous routes. When a request to send data is
made, the system must make routing decisions to determine a path for the
data.
The routing decisions are based on the network numbers listed in the
internal routing tables that are kept in the kernel. The internal routing
tables contain information on how to reach each host and network the
system knows about. The following section illustrates how a routing
decision is made.
1.1.5.1 A Simple Local Area Network Routing Exercise - Assume the
source host is oboe and the destination host is violin. The contents of
oboe's routing table are the value 98 for the network address and deO for
the interface to be used to reach network 98. Table 1-4 shows the
contents of oboe's /etc/hosts file.

Table 1-4: Host oboe's /etc/hosts File - Simple Configuration
Host

Address

oboe
violin
alto

98.65
98.70
98.42

Assume a user on oboe wants to perform a remote login to violin using
the rlogin command. The user types:
3 r I og in vi o I in

Here are the steps oboe follows to make the connection:
1.

2.
3.

1.1.6

The source host (oboe) needs to make a routing decision. Host
oboe learns from the /etc/hosts file that the final destination address
is on network 98. Therefore, oboe checks its internal routing tables
to find a route to network 98 and learns that network 98 is
connected to the Ethernet interface deO.
Because oboe is also connected to network 98, the data is put
directly onto the network wire, by way of the Ethernet.
Host violin picks up the data because it recognizes its own address in
the data packet.

Internet Networks

This section discusses a more complex network scheme called an Internet
network. An Internet network consists of two or more local area networks
connected together by a host acting as a gateway. This section explains
how to set up an Internet network. Figure 1-2 shows two networks and
several hosts.

Host
alto

Host
oboe
Network

98
Host
violin

Network
100
Host
cello

Host
guitar
ZK-0036U-HC

Figure 1-2: Two Networks and Several Hosts

An Internet network configuration operates in much the same manner as a
local area network with one Ethernet wire, except that a gateway is
needed. A gateway is a connection between two or more networks and
allows data to be transferred from a host on one network to a host on a
separate network.
The following three sections illustrate how to set up a gateway and use a
gateway to transfer data over an Internet network.
1.1.6.1 Setting Up a Gateway (Example) - Assume a user on alto
wants to execute a command on the remote host guitar. The user enters:
3 rsh guitar Is -als

The first step for alto is to look in its /etc/hosts file to obtain the Internet
address for guitar. Table 1-5 shows alto's /etc/hosts file.

Table 1-5: Host alto's /etc/hosts File - Internet Configuration
Host

Address

oboe
violin
alto
guitar
cello

98.0.0.65
98.0.0.70
98.0.0.42
100.0.0.35
100.0.0.37

From the /etc/hosts file, alto learns that guitar is on network 100. The
host alto's internal routing tables only have a route to network 98.
Because there is no physical connection between network 98 and network
100, a second interface is needed on host alto connecting alto to network
100. Then alto would be a gateway. Figure 1-3 shows how the two
networks would look after the gateway is established.

Host
oboe
Network

Host
alto

Network
100
Host
cello

Host
guitar
ZK-0037U-HC

Figure 1-3: Two Networks Connected by a Gateway Host (alto)

Note

Each hardware interface is connected to only one network. This
example assumes there are two hardware interfaces installed on
alto: one for network 98 and one for network 100.
This example shows how to set up alto as a gateway.
steps:

There are two

Modify the /etc/hosts file to include the new name for the connection
between alto and network 100.

Inform the system of the new route to network 100, using the
ifconfig command.

1.1.6.1.1 Edit the /etc/hosts File - The /etc/hosts file needs to be
updated to include an entry for the gateway's (alto) name and network
number. Table 1-6 shows the modified /etc/hosts file.

Table 1-6: Host alto's Modified /etc/hosts File - Internet Configuration
Host

Address

oboe
violin
alto
alto2
guitar
cello

98.0.0.65
98.0.0.70
98.0.0.42
100.0.0.42
100.0.0.35
100.0.0.37

Note that the host part of the address for alto2 is the same as the host
part for alto ( 42) . This is because alto2 and alto are the same host, but
one entry is on network 98 and the other is on network 100.
Note

It is not necessary for the host numbers associated with the
different interfaces to match, but it helps make the /etc/hosts file
more understandable.
Now the connection can now be made from alto to guitar in the same
manner as outlined in Section 1.1.5.1:

Host alto learns from the /etc/hosts file that the final destination
address is on network 100. Therefore, alto checks its internal routing
tables to find a route to network 100. It learns that network 100
can be reached by the del interface.

Because alto knows it is connected to network 100, it puts the data
directly onto the wire.

The destination host guitar picks up the data, because guitar
recognizes its own address.

1.1.6.1.2 Inform the System of the New Route - In this example, alto
is physically connected to network 100 as well as to network 98. To
inform the system of this information, the routing tables need to be
updated to include the route to network 100 by means of the new
interface.
Use the ifconfig command to inform the system of the network, using this
format:

ifconfig device-name name.
The ifconfig command uses the name to determine the network number of
the network to which the device is connected. If no broadcast address is
specified with the ifconfig command, the default broadcast address of the
network number followed by all ones ( 1) is assumed. See ifconfig( 8c) in
the UL TRIX Reference Pages for further information about the ifconfig
format.

In this example, a new name needs to be created that has 100 as the
network part of its Internet address. This host name will be added to the
/etc/hosts file. The ifconfig command can then use the name to obtain the
network number of the new connection to network 100.
The following example shows how to execute the ifconfig command, using
alto2 to establish a route to network 100:
# /etc/ifconf ig del alto2

Table 1-7 shows alto's modified routing table.

Table 1-7: Host alto's Internal Routing Table - Internet Configuration
Network

Interface

98
100

deO
del

Table 1-8 shows some of the common interface names.

Table 1-8: Common Interface Names
Name

Controller

DEUNA or DELUA (Ethernet)
DMR-11 or DMC-11 (point-to-point)
Q-bus (point-to-point)
DEQNA or DELQA (Ethernet)
DES VA (Ethernet)

dmc
dmv

qe
se
ni
scs

DEBNT or DEBNA (Ethernet)
pseudo device scsnet

1.1.6.2 Updating the Internal Routing Tables - The ifconfig command
updates the routing tables for the hosts where the interfaces reside. It
does not update the internal routing tables for the other hosts on the
networks that may need to know about the new gateway. Therefore, the
system manager on each host should follow these steps to update the
routing tables:

Edit the /etc/networks file.

Start the routed daemon or execute the route command to update
the routing tables.

1.1.6.2.1 Edit the /etc/networks File - Some of the network utility
commands, such as netstat, use the information contained in the
/etc/networks file. Here is what oboe's /etc/networks file should contain
after it is edited:
#
#

Internet networks

loop
ethernetl
ethernet2

127

98
100

loopback
doconet
devonet

The first field is the network name. For example, network 98 is also
known as ethernet1. The second field is the network number, and the
third field specifies network alias names.
1.1.6.2.2 Update the Routing Tables - The internal routing tables should
be updated each time the system is brought to multiuser mode. To do
this automatically, be sure the following entry is in the /etc/re. local file:
if

[

-f /etc/routed]; then
/etc/routed & echo -n ' routed'

>/dev/console

f i

This entry ensures that the tables are updated each time a host on the
network broadcasts pertinent information. This entry is executed each time
the system is brought to multiuser mode.
If this entry does not exist in the /etc/re.local file, you should edit

/etc/re.local and add it. The tables are updated automatically the next
time the system is booted.
To update the tables in the meantime, use the route command.
Note
If the routed daemon is already running on both systems and on

any needed gateways, there is no need to execute the route
command.
The following shows how to add the route to network 100, also known as
ethernet2, to oboe's internal routing tables, using the route command:
#

/etc/route add ethernet2 alto 1

In this example, you can specify either 100 or ethernet2. Note the
number 1 at the end of the entry. This is the metric value that
corresponds to the number of gateways needed to access the destination
host. A metric value must always be specified. The metric value indicates
the number of hops to the destination host, alto in this example. A
metric value of zero ( 0) indicates a direct connection with no 1:rntP.w::ivi;:

between the source host and the destination host. In this example, there
is only one gateway; therefore, the metric value is 1.
1.1.6.3 Using a Gateway - This section explains how to use a gateway
and builds upon examples used in Section 1.1.6.1.
Now that alto is established as a gateway, assume a user on oboe wants
to execute a remote command on guitar. The user enters:
% rsh guitar date

Assume that the contents of alto and oboe's /etc/hosts files are the same
(see Table 1-6). Here are the steps oboe takes:
1.

Host oboe learns from the /etc/hosts file that the final destination
address is on network 100. Therefore, oboe checks its internal
routing tables to find a route to network 100 and learns that alto is
a gateway to network 100.
When an entry exists in the internal routing tables, oboe knows to
send the data to alto, which is also connected to network 100. Host
alto then picks up the data.

Host alto learns from the address part of the message that the final
destination address is on network 100. Therefore, alto checks its
internal routing tables to find a route to network 100 and learns that
network 100 can be reached by the del interface.

Because alto knows it is connected to network 100 by way of the
del interface, alto puts the data directly onto the wire.

The destination host guitar picks up the data, because guitar
recognizes its own address.

1.2

Subnet Routing

Subnet routing allows numerous networks (subnetworks) to exist within a
given network. For example, network 98 could be made up of several
subnetworks. A host on a separate network could access all the hosts on
network 98 by going through the gateway connected to that network.
From there, the data is routed to the appropriate subnetwork, where the
destination host ultimately picks up its data, because it recognizes its own
address.
Subnetworks are useful for organizing hosts within a network into logical
groups. They expand the network name space of an Internet address and
allow several Ethernets to exist in the same logical network. For example,
if there are 10 hosts on one network, and three of the hosts are related to
research, three of the hosts are related to personnel, and four of the hosts

are related to marketing, it may be desirable to have three subnetworks
within the overall network. Subnetworks can save bits in the network part
of the Internet address, which is advantageous for a site with numerous
point-to-point links.
Subnet routing requires a slightly different interpretation of Internet
addresses. The bits in the host field of the Internet address are divided
into two groups: subnetwork and host. Instead of only two fields in the
Internet address, there are three: network, subnetwork, and host. By
taking bits from the host part of the address to make up the subnetwork
part, you can organize the bits so that the Internet addresses more closely
match your network environment.
The system does not know which bits in the host field are to be
interpreted as the subnetwork part of the Internet address, so a subnet
mask is needed.
1.2.1

Using Subnet Masks

The subnet mask is used to inform the system which bits of the Internet
address to interpret as the network and subnetwork addresses and which
bits to interpret as the host address.
A subnet mask is a 32-bit number. There is a one-to-one correspondence
between each of the 32 bits in the subnet mask and each of the 32 bits
in the Internet address.
For each bit in the subnet mask that is turned on (binary 1), the
corresponding bit position in the Internet address is interpreted as part of
the network and subnetwork address. For example, the decimal number
255 is 11111111 in binary notation, which means the entire 8-bit field is
turned on.
If the subnet mask bit position is part of the host field and is turned on,
then the corresponding bit in the Internet address is interpreted as part of
the subnetwork address. If the subnet mask bit position is part of the
host field and is turned off, then the corresponding bit in the Internet
address is interpreted as part of the host address.
Each bit in the first (left-most) field of the subnet mask must be turned
on (decimal value of 255, binary value of 11111111), because the first field
of the Internet address must always be interpreted as the network address,
regardless of whether there are subnetworks. If a bit in the first field of
the subnet mask were turned off, then part of the network field of ~he
Internet address would be interpreted as part of the host address. This
would cause errors, because each host must reside on a network.
The following two subnet masks are illogical. Note that a netmask entry
defines the subnet mask. The first entry interprets the entire Internet

address as the network address, leaving no bits to be interpreted as the
host address. The second entry interprets the entire Internet address as
the host address, leaving no bits to be interpreted as the network address:
netmask 255.255.255.255
netmask 0.0.0.0
Note

For each bit in the subnet mask that is turned off (binary 0),
the corresponding bit position in the Internet address is
interpreted as part of the host address. The decimal number 0
is 00000000 in binary notation. This means the entire 8-bit field
is turned off, because each bit position is a 0.
In general, the entire 8-bit field is turned either on ( 255) or off ( O). This
makes it easier for users to distinguish among the network, host, and
subnetwork fields.
Using the values 255 and 0 allows the fields to be divided evenly (into 8bit groups) between the subnetwork and host parts of the Internet address.
Values other than 255 and 0 do not divide evenly and, therefore, make the
host and subnetwork parts of the address more difficult to understand.
The first field of the subnet mask is always 255, so the system can
interpret the network number. The fourth field is usually 0, so the system
can interpret the host address. The second and third fields are usually
255 or 0, depending upon how the Internet address is to be interpreted.
Listed here are the valid values in decimal and binary notation for the two
middle fields of the network mask:
Decimal

Binary

255
254
252
248
240
224
192
128
0

11111111
11111110
11111100
11111000
11110000
11100000
11000000
10000000
00000000

Here are the most frequently used subnet mask values:

netmask 255.255.255.0
netmask 255.255.0.0
netmask 255.0.0.0

The way each of the fields is interpreted depends upon the network class,
as shown in Sections 1.2.1.1 and 1.2.1.2.
Note

Subnetworks are not appropriate for a Class C network, because
only eight bits are allocated for the host part of the Internet
address. Eight bits may not be enough to divide between a
subnetwork address and a host address.

1.2.1.1 Subnet Routing on a Class A Network (Example) - Assume
you have a subnet mask of 255.255.255.0 and assume the Internet address
is 98.0.1.65. The first digit of 98 in binary notation is 0 ( 98 in binary is
01100010), and 98 is in the range 0 through 127, so the Internet address
is on a Class A network.
In this example, the first three fields of the Internet address ( 98.0.1) are
interpreted as the network and subnetwork parts, and the fourth field ( 65)
is interpreted as the host part. Remember: only the host bits can be used
to represent a subnet number. Figure 1-4 shows how the Internet address
is interpreted in this example.

Subnet Mask

l Class-Type Network
Decimal
Binary

I
I
I
I
I
I
I

Subnetwork

255

11111111

Host

255

11111111

00000000

Internet Address
I

Decimal

Binary

01100010

l 00000000

I
I
I

00000001 : 01000001

ZK-0032U-HC

Figure 1-4: Interpreting a Class A Subnet Mask and Internet Address

The subnet mask and the Internet address in this example allow 8 bits to
define the network part, 16 bits to define the subnetwork part, and 8 bits
to define the host part of the Internet address. Therefore, the network
number is 98, the subnet number is 0.1, and the host address is 65.
1.2.1.2 Subnet Routing on a Class B Network (Example) - Assume
you have a subnet mask of 255.255.255.0, and assume the Internet address
is 128.0.2.42. The first two digits of 128 in binary notation are 10 ( 128
in binary is 10000000), and 128 falls in the range 128 through 191, so the
Internet address is on a Class B network.

In this example, the first two fields of the Internet address ( 128.0) are
interpreted as the network part. The third field ( 2) is interpreted as the
subnetwork part and the fourth field ( 42) is interpreted as the host part.
Figure 1-5 shows how the Internet address is interpreted in this example.

Subnet Mask
Class-Type

Network

Subnetwork

Host

Decimal

255

Binary

11111111

00000000

Decimal

128

Binary

10000000

00000000

00000010

00101010

Internet Address

ZK-0034U-HC

Figure 1-5: Interpreting a Class B Subnet Mask and Internet Address

The subnet mask and Internet address in this example allow 16 bits to
define the network, 8 bits to define the subnetwork, and 8 bits to define
the host of the Internet address. Therefore, the network number is '128.0,
the subnet number is 2, and the host number is 42.
1.2.1.3 Setting Up Subnetworks (Example) - This example, Figure 1-6,
shows how to connect two Ethernet subnetworks together by way of a
point-to-point link. The netmask parameters, which specify the subnet
mask in the ifconfig command, are introduced.
Assume the source host is flute and the destination host is piano, they are
connected to the local area network number 75, and the subnet mask is
255.255.0.0.

75.1
(subnetwork)
deO flute 75.1.0.11

flute

dmcO flute 2 75.3.0.11

piano

IdeO piano 75.2.0.15
75.2
(subnetwork)

ZK-0031 U-HC

Figure 1-6: Subnetwork Configuration with Point-to-Point Links

Before flute can send data to piano, flute's /etc/hosts file and internal
routing table must be updated to contain the information about piano.
1.2.1.3.1 Edit the /etc/hosts File - Host flute's /etc/hosts file needs to
be updated to include an entry for the name of the connection to subnet
75.3 ( flute2). Table 1-9 shows the updated /etc/hosts file.

Table 1-9: Host flute's Updated /etc/hosts File

Host

Address

flute
piano
flute2
piano2

75.1.0.11
75.2.0.15
75.3.0.11
75.3.0.15

1.2.1.3.2 Inform the System of the New Routes - In this example,
flute is physically connected to network 75.3 as well as to network 75.1.
Use the ifconfig command to update the routing tables to include the
interfaces and hosts. In the following commands, flute2 is the name of the
connection to subnetwork 75.3:
# /etc/ifconfig deO flute broadcast 75.1.255.255 netmask 255.255.0.0
# /etc/ifconf ig dmcO flute2 piano2 netmask 255.255.0.0

Subnetwork 75.3 consists of two hosts connected by a point-to-point link.
Because point-to-point links always connect two hosts directly together, the
ifconfig command needs to include the two connected host names, but does
not need to include a broadcast address. For further information, see
ifconfig( 8c) in the ULTRIX Reference Pages
Table 1-10 shows flute's updated internal routing table.

Table 1-10: Host flute's Updated Internal Routing Table
Network

Interface

Gateway

75.1
75.3
75.2

deO
dmcO
dmcO

piano

The last entry in Table 1-10 is for the route to network 75.2, which flute
learned of from the /etc/routed daemon.

The ifconfig command is used to supply the system with the subnet mask.
Data can now be transferred from flute to piano in exactly the same
manner as outlined in Section 1.1.5.1:
1.

Host flute checks its /etc/hosts file to obtain the Internet address for
piano. From the /etc/hosts file, flute learns that it is on network
75.1 and that piano is on network 75.2. Although flute and piano
are on different subnetworks, flute is set up as a gateway to
subnetwork 75.3. This example assumes that the system manager on
piano previously set up piano as a gateway.
Note

For point-to-point links, such as are needed by DMR-11
interfaces, both ends of the link must be set up as
gateways.
2.

Host flute checks its internal routing tables to find a route to
subnetwork 75.3, and learns that subnetwork 75.3 can be reached by
the dmcO interface.

Because flute knows it is connected to subnetwork 75.3, it passes the
data directly to the DMR-11 interface.

The destination host piano picks up the data.

1.3

Loca I Area Network Files

This section describes the files that are created when you install a local
area network. The files are:

•
•
•
•
•
•
•
•
•
•
•

/etc/inetd.conf
/etc/protocols
/etc/services
/etc/networks
/etc/re
/etc/hosts
/etc/hosts.equiv
.rhosts
/etc/re.local
/usr/hosts
/usr/spool/rwho

1.3.1

The /etc/inetd.conf File

The /etc/inetd.conf file contains information regarding the standard services
that inetd processes by opening sockets and listening for requests. You do
not need to modify the /etc/inetd.conf file unless you want to add a
nonstandard service or remove a service from your local area network.
As distributed, the /etc/inetd.conf file contains entries for the standard
services, with the following services enabled:
•

•

shell

•

exec

•

talk

•
•

time
ftp

The services that you should include in /etc/inetd.conf and use on your
system depend on the size of your system configuration. On most
systems, however, the minimum services are: login or telnet, shell, exec,
and talk.
On systems with sufficient memory, you can, in order of their importance,
include: time, ftp, and tfpt.
Note

Because tftp does not require user authentication, it is not very
secure. Therefore, you should include it in /etc/inetd.conf only if
it is needed.
To add a nonstandard service, edit the /etc/inetd.conf file and create a new
entry. To comment out an existing service, edit the /etc/inetd.conf file and
insert a comment character ( #) at the beginning of the appropriate entry.
For the format of the /etc/inetd.conf file, see inetd.conf( 5) in the ULTRIX
Reference Pages.
1.3.2

The /etc/protocols File

The /etc/protocols file contains information regarding the known protocols
used in the Internet. You do not need to modify the /etc/protocols file
unless you want to add a nonstandard Internet protocol to your local area
network. See protocols( 5) in the ULTRIX Reference Pages for information
on the format of the /etc/protocols file.

1.3.3

The /etc/services File

The /etc/services file contains information regarding the known services
available in the Internet. You do not need to modify the /etc/services file
unless you want to add a nonstandard Internet service to your local area
network. See services( 5) in the ULTRIX Reference Pages for information
on the format of the /etc/services file.
1.3.4

The /etc/networks File

The /etc/networks file contains information regarding the known networks
that compose the Internet. You do not need to modify the /etc/networks
file unless you want to add or remove a network from your system. See
networks( 5) in the ULTRIX Reference Pages for information on the format
of the /etc/networks file.
1.3.5

The /etc/re and /etc/re.local Files

As distributed, the /etc/re and /etc/re.local files list a number of entries
that are used to set up the network when the system is brought to
multiuser mode. More specifically, the /etc/re and /etc/re.local files:
•
•

Initialize the loopback device
Initialize the network device

•

Start network daemons

If you are using the network, the /etc/re and or /etc/re.local file starts

these daemons:

•
•
•
•
•

syslog
routed
inetd
rwho
send mail

As it starts up each daemon, the /etc/re or /etc/re.local file echoes to the
console the name of the daemon. Therefore, while your system is going to
multiuser mode, your console lists those daemons that currently are up and
running.
As distributed, the /etc/re.local file does not set the date and time from
the network. If you want the date and time to be set, edit the
/etc/re.local file and remove the comment character ( #) from the beginning
of the line that lists the /etc/rdate entry.
If you have a number of systems on your network, you can turn off the

performance. In addition, if you are using a single wire network, you can
turn off the routed daemon. In any case, the minimum network daemons
to be started from the /etc/re and /etc/re.local files are:
•

syslog

•

inetd

•

send mail

Your system can be connected to more than one network. The /etc/re.local
file contains initialization information regarding the various networks to
which your system is connected. The first entry in the re. local file should
be for the primary network interface.
If you add a network interface, such as a DEUNA, then you need to add
an ifconfig line to the /etc/re.local file.

The re.local file also needs an entry for the loopback interface, which
usually follows all the network interface entries. The loopback interface
allows connections between programs on the same host.
The following are example lines from an /etc/re.local file specifying two
DEUNA interfaces, a DMR-11 interface, and a loopback interface:
/etc/ifconfig
/etc/ifconfig
/etc/ifconfig
/etc/ i fconf i g

deO '/bin/hostname' broadcast 128.45.255.255 netmask 255.255.0.0
dmcO oboe2 piano2 netmask 255.255.0.0
del oboe3
broadcast 98.1.255.255 netmask 255.255.0.0
I oO I oca I host

Note that the entries configure systems on two different network classes.
You can tell this by the network addresses ( 128.45.255.255 is on a class B
network, 98.1.255.255 is on a class A network). Note that oboe now has
three hardware interfaces and one software (loopback) interface.
Because the first device to be configured becomes the default network
device for sockets, it is important that the loopback driver be configured
after the real network devices. In most cases, the default network should
not be the local loopback pseudodevice.
1.3.6

The /etc/hosts File

The /etc/hosts file contains a list of the known hosts on the Internet
network. It contains the official system names, identification numbers, and
nodes. To add a host system to your local area network, add an entry for
that system to the /etc/hosts file. Likewise, to remove a host system from
your local area network, delete that system's entry from the /etc/hosts file.
See hosts( 5) in the ULTRIX Reference Pages for information on the
format of the /etc/hosts file.

1.3. 7

The /etc/hosts.equiv File

The /etc/hosts.equiv file allows the general users (not root) of a remote
system to log in to your system without supplying a password, provided
the remote system has an entry in hosts.equiv and the user has an
account on your system. The /etc/hosts.equiv file lists, one system name
per line, all the systems that are considered logically equivalent to your
local system.
For security reasons, the logically equivalent systems are usually run by
the same administration.
A system included in the /etc/hosts.equiv file is treated exactly the same
as the local system is treated. This means the logically equivalent system
has all the privileges that the local system has. Note that the
/etc/hosts.equiv file has impact on the destination system only. That is,
the access is always checked on the destination system. Thus, it is
possible for systema to be logically equivalent to systemb, although systemb
is not logically equivalent to systema.
The /etc/hosts.equiv file allows all the users of a remote system to log in
to your system without supplying a password, except for the superuser and
those users who do not have an account on your system. You can grant
the login privilege to a small number of users, including the superuser, on
a remote site by using the . rhosts file.
1.3.8

The .rhosts File

The .rhosts file can exist in each user's home directory. It allows an
individual user from a remote system to log in to your system without
supplying a password. You must first create an account for the remote
user on your system. The user then needs to put a . r~osts file in his or
her home directory on the remote system.
The format of the . rhosts file is:

hostname user-id
The host name is the name of the remote system (the user's local
system), and the user ID is the user's login name. For example, the
proper entry for a person from systema with a login name of guest is:
systema guest

If no user ID is specified on the line, then the user must have the same

Although it is not a recommended practice, you can allow the
superuser of a remote system to log in to your system without
password protection by having a . rhosts file in the root ( !)
directory.
In addition to having a .rhosts file, the superuser needs a secure
terminal entry in the /etc/ttys file for each pseudoterminal configured
in the system. The entry for the superuser should be something like
this:
ttyp3

none network

secure

See ttys( 5) in the ULTRIX Reference Pages for information about the
/etc/ttys file.

1.3.9

The /usr/hosts Directory

If the /usr/hosts directory is included in a user's search path in the .login
or .profile file, the user can log in to a remote host by typing only the

name of that system instead of:
# rlogin host

For example, assuming there is an entry in the /usr/hosts directory for
flute and assuming the user has this directory included in the search path,
the user can type the following to log in to the remote system flute:
3 flute

For a user to be able to log in to a remote host without using the rlogin
command, the superuser (root) must execute the /usr/hosts/MAKEHOSTS
command after the network has been set up and is operational. In
addition, the superuser must execute the /usr/hosts/MAKEHOSTS command
each time a new host is added to the network.
1.3.10

The /usr/spool/mqueue Directory

The /usr/spool/mqueue directory contains the network syslog files. Each
syslog file ·contains the daemon error messages and information from
utilities such as sendmail, the remote installation, Ethernet remote node
maintenance functions, and so forth, that occurred during a day's operation.
The syslog files are automatically maintained by the /usr/adm/newsyslog
program, which is executed once a day by /etc/cron. Normally, you do not
have to alter the times when /usr/adm/newsyslog is executed. However, if

you want to run /usr/adm/newsyslog more often or less often, edit
/usr/lib/crontab and make the appropriate time changes.
See cron( S) in the ULTRIX Reference Pages for information on the format
of the /usr/lib/crontab file.
1.3.11

The /usr/spool/rwho Directory

The /usr/spool/rwho directory contains a file named whod.system-name for
each system connected to your local area network. The data for the rwho
and ruptime commands is saved in this directory.
If you remove a system from your local network, you should remove that
system's file from the /usr/spool/rwho directory. This clears the directory
of unneeded files and helps keep the rwho and ruptime information up to
date.

1.4

Network Maintenance Commands

These commands are helpful in the event that you encounter problems with
the network:
arp

Displays and modifies the Internet-to-Ethernet address
translation tables that the address resolution protocol uses.
For further information, see arp( 4p) and arp( Sc) in the
ULTRIX Reference Pages.

ifconfig

Assigns an address to a network interface and/or configures
the network interface parameters. You can use ifconfig to
redefine an interface's address, but you should not change the
addresses while the system is running. For further
information, see ifconfig( Sc) in the ULTRIX Reference Pages.

netstat

Displays the contents of various network-related data
structures. If no options are specified, netstat displays the
state of all active sockets from those using any of the
protocols listed in the /etc/protocols file. For further
information, see netstat( 1) in the ULTRIX Reference Pages.

Setting Up a Local Area Network 2

This chapter describes how to set up your system on a local area network
(LAN) and how to update the /etc/hosts and /etc/hosts.equiv files using the
netsetup command. The steps described here assume you are familiar with
local area networks. If you need further information about local area
networks, see Chapter 1.
The setup procedures described in this chapter are:
•

Adding your system to an existing local area network

•

Setting up a local area network

•

Setting up an Internet network with gateways

•

Setting up a local area network with subnet routing

•

Updating your local area network
Note
If you are already running YP on your system, read the Guide

to the Yellow Pages Service for information on how to modify
YP maps before you run the netsetup command. You will need
to modify the hosts, hosts.equiv, networks, and protocols files
manually.
You can use the Berkeley Internet Name Domain (BIND) service
to obtain host names and addresses from BIND servers, and to
replace or supplement the host table mapping provided by the
local /etc/hosts file or the Yellow Pages ( YP) service. See the
ULTRIX-32 Guide to the BIND Service for detailed information
and procedures.

2.1

Adding Your System to an Existing Local Area
Network

This section describes how to add your system to an existing local area
network using the netsetup command.

2.1.1

Prerequisite Information

Before executing netsetup, you must know the answers to the following
questions. The network manager for the local area network should provide
you with this information:
•
•

What is your system's Internet address?
Which part of your Internet address is the network address ( network
number), and which part is the host address (host number)?
If you know the network class of the local area network, you can
calculate the network and host addresses from the Internet address,
as described in Chapter 1.

•

What is your Internet Protocol (IP) broadcast address? Does the
existing local area network use all zeros ( 0) or all ones ( 1)? See
Chapter 1 for information about IP broadcast addresses.

•

Does the existing local area network use subnet routing? If the
answer is yes, then how many bits of the host part of the Internet
address are used to specify the subnet part of the network address?

•

What are the host name and Internet address of the other hosts on
the existing local area network?

When you have the answers to these questions, you are ready to set up
your local area network.
2.1.1.1 Run the netsetup Command - Run the netsetup command with
the install option:
# /etc/netsetup

instal I

The word install tells netsetup that this is a first-time installation.
When netsetup is running, it prints the following information and prompt:
You wi I I be asked a series of questions about your system.
Default answers are shown in square brackets ([]).
To use a default answer, press the RETURN key.
Your system's name is

systeml

•

Is this correct [yes]?

In this example, system1 is the name of the host. The host name
displayed should be the system name declared when your system was
installed. If this is the case, answer yes or press the RETURN key. If
this is not your host name, answer no. The netsetup program then
prompts for your correct host name.
The netsetup command asks a series of questions about your local system
and the network. You should supply the answers you obtained from the
network manager.

When netsetup has completed making the required modifications, it prints
this informational message:
***** NETWORK SETUP COMPLETE *****
Note
If you need to terminate the netsetup command before it has
completed, you can press CTRL/C. However, some of the network
files may already be modified. You should run netsetup again, to
completion, so you have a known state of the network files and
directories.

2.1.1.2 Reboot System to Effect Changes - If you add your system to
a local area network with the netsetup command while the system is in
multiuser mode, your system will not be established on the network until
the system is brought to multiuser mode again by rebooting the system.

2.2

Setting Up a Local Area Network

This section describes how to set up a new local area network using the
netsetup command. If you want the simplest network configuration, then
select the following options:
•

Choose a Class A network

•

Do not use subnetworks

•

Use an Internet broadcast address of all ones
Note

It is wise to obtain a registered Internet address, even if you do
not intend to connect your network to an outside one. Then, if
you choose to connect to another network in the future, such as
the Arpanet, you will not need to change all your IP addresses.
To obtain a registered IP address application, call the Network
Information Center at 800-235-3155 or 415-859-3695.
If you have access to the Arpanet, you can send mail to:
nic@sri-nic.arpa

2.2.1

Prerequisite Information

Before executing netsetup, you must know the answers to the following
questions. If you are creating your own local area network, you can choose
any Internet address, network number, and host number you like, provided
that your numbers comply with the networking requirements described in
Chapter 1.
•

What is your system's Internet address?

•

What part of your Internet address is the network address (network
number), and which part is the host address (host number)?

•

What is your Internet Protocol (IP) broadcast address? You should
use all ones ( 1). See Chapter 1 for information about IP broadcast
addresses.

•

Will your local area network be using subnet routing? To keep your
network simple, do not use subnet routing unless necessary.
What are the host names and Internet addresses of the other hosts
you will be adding to the local area network?

After you have the answers to these questions, you are ready to set up
your local area network. Follow the four steps described in Section 2.1.1.

2.3

Setting Up an Internet Network with Gateways

An Internet network is two or more local area networks connected. The
Internet network uses some of the hosts as gateways. To set up a new
local area network with gateways, you must do two things:
1.
2.

Set up a new local area network
Establish a host as a gateway

You must know which host will be the gateway. If a host on a different
local area network will be acting as the gateway to your local area
network, you must know this in advance.
2.3.1

Set Up a Local Area Network

To set up a basic local area network, follow these steps:
1.

Bring the system to single-user mode

Mount the /usr partition

Run the netsetup command

These steps are described in Sections 2.1.1.1, 2.1.1.2, and 2.1.1.3.
However, do not execute the step described in Section 2.1.1.4, "Bring the
System to Multiuser Mode" when netsetup is completed. Instead, go to
Section 2.3.2.

2.3.2

Establish a Host as a Gateway

If a host other than your own system will be acting as the gateway, be
sure there is an entry in your /etc/hosts file for that host. You probably
already made the entry when you created your local area network with the
netsetup command. If you did not, you can edit /etc/hosts manually.
Then, reboot your system and the task is complete.

To set up your own system as a gateway, follow these steps:
1.

Inform your system of the new route
Your system must be physically connected to two or more networks.
However, it only knows about the network number you entered while
using the netsetup command. Because a host cannot be connected to
more than one network, you must choose a pseudohost name. For
example, if your system's name is alto, you might choose A2. as its
pseudohost name. You should obtain the network number of the
other local area network from the network manager. To inform
your system of the new route, use this form of the ifconfig command:
/etc/ifconfig device-name pseudohost-name

For example, to set up A2. as a pseudohost on a DEUNA, type:
#

/etc/ifconfig del A2

Edit the /etc/hosts file.
Add an entry for the gateway host, specifying the pseudohost name
and network number.

Bring the system to multiuser mode.
When the system is brought to multiuser mode, the gateway is
established. To bring the system to multiuser mode, press CTRL/D:
# cd I
# /etc/umount /usr
# <CTRL/D>

For further information about setting up gateways, see Chapter 1.

2.4

Setting Up a Local Area Network With Subnet
Routing

A local area network with subnetworks is similar to a local area network
with gateways. However, unlike the hosts on an Internet network, each of
the hosts on a network with subnet routing has the same network number.
This section describes how to use the netsetup command to set up a new
local area network with subnet routing.

If you are setting up a new local area network, choose either a Class A or
Class B network. Class C networks rarely use subnet routing. In
addition, use an Internet broadcast address of all ones.
2.4.1

Prerequisite Information

Before executing netsetup, you must know the answers to the following
questions. If you are creating your own local area network, you can choose
any Internet address, network number, subnet number, and host number
you like, provided that your numbers comply with the networking
requirements described in Chapter 1.
•

What is your system's Internet address?

•

What part of your Internet address is the network address (network
number), the host address, and subnet address (host number)?
When you supply the host address to netsetup, be sure that you
include the subnet address.

•

What is your Internet Protocol (IP) broadcast address? You should
use all ones ( 1). See Chapter 1 for information about IP broadcast
addresses.

•

Will your local area network be using subnet routing?
yes.

•

How many bits of the host part of the Internet address are used to
specify the subnet part of the network address? If you plan to use
the common method of notating the Internet address, you may want
to use 8 bits, but this depends on how you plan to use your local
area network. See Chapter 1 for further information about Internet
addresses.

The answer is

What are the host names and Internet addresses of the other hosts
you will be adding to the local area network?
After you have the answers to these questions, you are ready to set up
your local area network. Follow the four steps described in Section 2.1.1.

2.5

Updating Your Local Area Network

If a local area network is already set up on your system and you want to
add a new host or new trusted host, run the netsetup command with no
options:

# /etc/netsetup

By omitting the word install, netsetup updates the existing /etc/hosts and
/etc/hosts.equiv files. When netsetup is running, it prompts for the new
host names to be added to the /etc/hosts and /etc/hosts.equiv files.
If you need to make any modifications to network files other than adding

hosts or trusted hosts, you need to edit the appropriate file as explained in
Chapter 1.
Note

There is no need to bring your system to single-user mode before
running netsetup to update the /etc/hosts and /etc/hosts.equiv
files.
If your system is running YP, see the Guide to the Yellow Pages
Service. before you run the netsetup command. This guide
describes how to modify the hosts, hosts.equiv and other

network-related files.

Index

c
Class A network
network class, 1-7
specifying, 1-3
Class B network
network class, 1-7
specifying, 1-4
Class C network
network class, 1-7
specifying, 1-4

G
gateway
defined, 1-10
establishing your system as, 2-4
point-to-point links and, 1-23n
setting up, 1-10 to 1-14
using, 1-16

H
host
See also pseudohost
defined, 1-2
hosts directory, 1-28
hosts.equiv file
See also .rhosts file
description, 1-27
hosts file
adding host system, 1-27
contents, 1-2
removing host system, 1-27
specifying subnetwork, 1-22

inetd.conf file
default entries, 1-24, 1-25
modifying, 1-24
tftp and, 1-25n
internal routing table
adding subnetwork, 1-22
updating, 1-14 to 1-16
Internet address, 1-2 to 1-5
See also Internet broadcast address
alternate notation, 1-4 to 1-5
common notation, 1-3 to 1-4
defined, 1-2
format, 1-5t
registering, 1-3n, 2-3n
Internet broadcast address
default format, 1-8
defined, 1-8
Internet network
compared to local area network, 110
defined, 1-9
setting up, 1-9 to 1-14, 2-4 to 2-5
IP address
See Internet address

LAN
See local area network
local area network
adding host, 2-6
adding your system, 2-1 to 2-3
defined, 1-1

introduction, 1-1 to 1-16
overview, 1-1 to 1-30
related files, 1-23 to 1-30
routing decisions, 1-8
routing example, 1-9
setting up, 2-1 to 2-6
setting up with subnet routing, 2-5
to 2-6
simple configuration, 1-2f
loopback address
reserved, 1-4n

M
mqueue directory, 1-29

N
netmask
See subnet mask
netsetup command
running, 2-6
terminating, 2-3n
YP and, 2-ln
network
maintenance commands, 1-29
network class
binary range, 1-6t
decimal range, 1-6t
determining, 1-5 to 1-8
network field
defined, 1-5
networks file
contents, 1-2
modifying, 1-25
updating, 1-15
newsyslog program
setting execution time, 1-29

p
point-to-point link
defined, 1-8
protocols file
modifying, 1-25
pseudohost
establishing, 2-5

R
re file, 1-25 to 1-27
default entries, 1-25
modifying, 1-25
re.local file, 1-25 to 1-27
adding loopback interface, 1-26
adding network interface, 1-26
default entries, 1-25
modifying, 1-25
remote host
logging in, 1-28
.rhosts file
See also hosts.equiv file
creating, 1-28
remote system superuser and, 128n
rwho directory
contents, 1-29

s
services file
modifying, 1-25
subnet mask, 1-17 to 1-23
Class A network and, 1-19 to 1-20
Class B network and, 1-20
Class C network and, 1-19n
frequently used values, 1-18
point-to-point links and, 1-21 to 123

subnet routing
introduction, 1-16 to 1-23
syslog file
contents, 1-29
system date
setting, 1-26
system time
setting, 1-26

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