TCP/IP Configuration Files
Each system on the network obtains its TCP/IP configuration information from the following
TCP/IP configuration files and network databases:
/etc/defaultrouter file (optional)
netmasks database (optional)
The Solaris installation program creates these files as part of the installation process.
You can also edit the files manually, as explained in this section. The
hosts and netmasks databases are two of the network databases read by the
name services available on Solaris networks. Network Databases and the nsswitch.conf File describes in detail the concept of
network databases. .
This file defines the physical network interfaces on the local host. At least
one /etc/hostname.interface file should exist on the local system. The Solaris installation program
creates an /etc/hostname.interface file for the first interface that is found during the installation
process. This interface usually has the lowest device number, for example eri0, and is
referred to as the primary network interface. If the installation programs finds additional interfaces, you
optionally can configure them, as well, as part of the installation process.
If you add a new network interface to your system after installation, you
must create an /etc/hostname.interface file for that interface, as explained in How to Configure a Physical Interface After System Installation. Also,
for the Solaris software to recognize and use the new network interface, you
need to load the interface's device driver into the appropriate directory. Refer to
the documentation that comes with the new network interface for the appropriate interface
name and device driver instructions.
The basic /etc/hostname.interface file contains one entry: the host name or IPv4 address
that is associated with the network interface. The IPv4 address can be expressed
in traditional dotted decimal format or in CIDR notation. If you use a
host name as the entry for the /etc/hostname.interface file, that host name must also
exist in the /etc/inet/hosts file.
For example, suppose smc0 is the primary network interface for a system that
is called tenere. The /etc/hostname.smc0 file could have as its entry an
IPv4 address in dotted decimal notation or in CIDR notation, or the host
name tenere .
Note - IPv6 uses the /etc/hostname6.interface file for defining network interfaces. For more information, refer
to IPv6 Interface Configuration File.
This file should contain one entry: the host name of the local system.
For example, on system timbuktu, the file /etc/nodename would contain the entry
This file should contain one entry: the fully qualified domain name of the
administrative domain to which the local host's network belongs. You can supply this
name to the Solaris installation program or edit the file at a later
date. For more information on network domains, refer to System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP).
This file can contain an entry for each router that is directly connected
to the network. The entry should be the name for the network
interface that functions as a router between networks. The presence of the /etc/defaultrouter
file indicates that the system is configured to support static routing.
The hosts database contains the IPv4 addresses and host names of systems on
your network. If you use the NIS or DNS name service, or the
LDAP directory service, the hosts database is maintained in a database that is
designated for host information. For example, on a network that runs NIS, the
hosts database is maintained in the hostsbyname file.
If you use local files for the name service, the hosts database is
maintained in the /etc/inet/hosts file. This file contains the host names and IPv4
addresses of the primary network interface, other network interfaces that are attached to
the system, and any other network addresses that the system must check for.
Note - For compatibility with BSD-based operating systems, the /etc/hosts file is a symbolic link to
/etc/inet/hosts File Format
The /etc/inet/hosts file uses the basic syntax that follows. Refer to the hosts(4)
man page for complete syntax information.
IPv4-address hostname [nicknames] [#comment]
Contains the IPv4 address for each interface that the local host must recognize.
Contains the host name that is assigned to the system at setup, plus the host names that are assigned to additional network interfaces that the local host must recognize.
Is an optional field that contains a nickname for the host.
Is an optional field for a comment.
Initial /etc/inet/hosts File
When you run the Solaris installation program on a system, the program configures
the initial /etc/inet/hosts file. This file contains the minimum entries that the local
host requires. The entries include the loopback address, the host IPv4 address, and
the host name.
For example, the Solaris installation program might create the following /etc/inet/hosts file
for system tenere shown in Figure 5-1:
Example 10-1 /etc/inet/hosts
File for System tenere
127.0.0.1 localhost loghost #loopback address
192.168.200.3 tenere #host name
In Example 10-1, the IPv4 address 127.0.0.1 is the loopback address. The loopback address is the
reserved network interface that is used by the local system to allow interprocess
communication. This address enables the host to send packets to itself. The ifconfig
command uses the loopback address for configuration and testing, as explained in Monitoring the Interface Configuration With the ifconfig Command.
Every system on a TCP/IP network must use the IP address 127.0.0.1
for IPv4 loopback on the local host.
The IPv4 address 192.168.200.1 and the name tenere are the address and
host name of the local system. They are assigned to the system's primary
Multiple Network Interfaces
Some systems have more than one network interface, because they are either routers
or multihomed hosts. Each network interface that is attached to the system requires
its own IP address and associated name. During installation, you must configure the
primary network interface. If a particular system has multiple interfaces at installation time,
the Solaris installation program also prompts you about these additional interfaces. You can
optionally configure one or more additional interfaces at this time, or manually, at
a later date.
After Solaris installation, you can configure additional interfaces for a router or multihomed
host by adding interface information to the systems' /etc/inet/hosts file. For more
information on configuring routers and multihomed hosts refer to Configuring an IPv4 Router and Configuring Multihomed Hosts.
Example 10-2 shows the /etc/inet/hosts file for system timbuktu that is shown in Figure 5-1.
Example 10-2 /etc/inet/hosts
File for System timbuktu
127.0.0.1 localhost loghost
192.168.200.70 timbuktu #This is the local host name
192.168.201.10 timbuktu-201 #Interface to network 192.9.201
With these two interfaces, timbuktu connects networks 192.168.200 and 192.168.201 as a router.
How Name Services Affect the hosts Database
The NIS and DNS name services, and LDAP directory service, maintain host names
and addresses on one or more servers. These servers maintain hosts databases
that contain information for every host and router (if applicable) on the servers'
network. Refer to System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP) for more information about these services.
When Local Files Provide the Name Service
On a network that uses local files for the name service, systems that
run in local files mode consult their individual /etc/inet/hosts files for IPv4 addresses
and host names of other systems on the network. Therefore, these system's /etc/inet/hosts
files must contain the following:
IPv4 address and host name of the local system (primary network interface)
IPv4 address and host name of additional network interfaces that are attached to this system, if applicable
IPv4 addresses and host names of all hosts on the local network
IPv4 addresses and host names of any routers that this system must know about, if applicable
IPv4 address of any system your system wants to refer to by its host name
Figure 10-1 shows the /etc/inet/hosts file for system tenere. This system runs in local files
mode. Notice that the file contains the IPv4 addresses and host names for
every system on the 192.9.200 network. The file also contains the IPv4 address
and interface name timbuktu-201. This interface connects the 192.9.200 network to the 192.9.201
A system that is configured as a network client uses the local
/etc/inet/hosts file for its loopback address and IPv4 address.
Figure 10-1 /etc/inet/hosts File for a System Running in Local Files Mode
You need to edit the netmasks database as part of network configuration only
if you have set up subnetting on your network. The netmasks database consists of
a list of networks and their associated subnet masks.
Note - When you create subnets, each new network must be a separate physical network.
You cannot apply subnetting to a single physical network.
What Is Subnetting?
Subnetting is a method for maximizing the limited 32-bit IPv4 addressing space and
reducing the size of the routing tables in a large internetwork. With any
address class, subnetting provides a means of allocating a part of the host
address space to network addresses, which lets you have more networks. The part
of the host address space that is allocated to new network addresses is
known as the subnet number.
In addition to making more efficient use of the IPv4 address space, subnetting
has several administrative benefits. Routing can become very complicated as the number of
networks grows. A small organization, for example, might give each local network a
class C number. As the organization grows, the administration of a number of
different network numbers could become complicated. A better idea is to allocate a
few class B network numbers to each major division in an organization. For
example, you could allocate one Class B network to Engineering, one Class B
to Operations, and so on. Then, you could divide each class B network
into additional networks, using the additional network numbers gained by subnetting. This division
can also reduce the amount of routing information that must be communicated among
Creating the Network Mask for IPv4 Addresses
As part of the subnetting process, you need to select a network-wide
netmask. The netmask determines how many and which bits in the host address
space represent the subnet number and how many and which bits represent the
host number. Recall that the complete IPv4 address consists of 32 bits. Depending
on the address class, as many as 24 bits and as few as
8 bits can be available for representing the host address space. The
netmask is specified in the netmasks database.
If you plan to use subnets, you must determine your netmask before
you configure TCP/IP. If you plan to install the operating system as part
of network configuration, the Solaris installation program requests the netmask for your network.
As described in Designing an IPv4 Addressing Scheme, 32-bit IP addresses consist of a network part
and a host part. The 32 bits are divided into 4 bytes. Each
byte is assigned to either the network number or the host number, depending
on the network class.
For example, in a class B IPv4 address, the 2 bytes on
the left are assigned to the network number, and the 2 bytes on
the right are assigned to the host number. In the class B IPv4
address 172.16.10, you can assign the 2 bytes on the right to hosts.
If you are to implement subnetting, you need to use some of
the bits in the bytes that are assigned to the host number to
apply to subnet addresses. For example, a 16-bit host address space provides addressing
for 65,534 hosts. If you apply the third byte to subnet addresses and
the fourth byte to host addresses, you can address up to 254 networks,
with up to 254 hosts on each network.
The bits in the host address bytes that are applied to subnet
addresses and those applied to host addresses are determined by a subnet mask. Subnet masks
are used to select bits from either byte for use as subnet
addresses. Although netmask bits must be contiguous, they need not align on byte
The netmask can be applied to an IPv4 address by using the
bitwise logical AND operator. This operation selects out the network number and subnet number
positions of the address.
Netmasks can be explained in terms of their binary representation. You can use
a calculator for binary-to-decimal conversion. The following examples show both the decimal and
binary forms of the netmask.
If a netmask 255.255.255.0 is applied to the IPv4 address 172.16.41.101, the result
is the IPv4 address of 172.16.41.0.
172.16.41.101 & 255.255.255.0 = 172.16.41.0
In binary form, the operation is as follows:
10000001.10010000.00101001.01100101 (IPv4 address)
Now the system looks for a network number of 172.16.41 instead of a
network number of 172.16. If your network has the number 172.16.41, that number
is what the system checks for and finds. Because you can assign up
to 254 values to the third byte of the IPv4 address space, subnetting
lets you create address space for 254 networks, where previously space was available
for only one.
If you are providing address space for only two additional networks, you can
use the following subnet mask:
This netmask provides the following result:
This result still leaves 14 bits available for host addresses. Because all 0s
and 1s are reserved, at least 2 bits must be reserved for
the host number.
If your network runs NIS or LDAP, the servers for these name
services maintain netmasks databases. For networks that use local files for the name service,
this information is maintained in the /etc/inet/netmasks file.
Note - For compatibility with BSD-based operating systems, the /etc/netmasks file is a symbolic
link to /etc/inet/netmasks.
The following example shows the /etc/inet/netmasks file for a class B network.
Example 10-3 /etc/inet/netmasks
File for a Class B Network
# The netmasks file associates Internet Protocol (IPv4) address
# masks with IPv4 network numbers.
# network-number netmask
# Both the network-number and the netmasks are specified in
# “decimal dot” notation, e.g:
# 220.127.116.11 255.255.255.0
If the /etc/netmasks file does not exist, create it with a text editor.
Use the following syntax:
Refer to the netmasks(4) man page for complete details.
When creating netmask numbers, type the network number that is assigned by the
ISP or Internet Registry (not the subnet number) and the netmask number in
/etc/inet/netmasks. Each subnet mask should be on a separate line.
You can also type symbolic names for network numbers in the /etc/inet/hosts
file. You can then use these network names instead of the network numbers
as parameters to commands.