hosts Database

The hosts database contains the IP addresses and host names of machines on your network. If you use the NIS, NIS+, or DNS name services, the hosts database is maintained in a database designated for host information. For example, on a network running NIS+, the hosts database is maintained in the host table.

If you use local files for name service, the hosts database is maintained in the /etc/inet/hosts file. This file contains the host names and IP addresses of the primary network interface, other network interfaces attached to the machine, and any other network addresses that the machine must know about.

For compatibility with BSD-based operating systems, the file /etc/hosts is a symbolic link to /etc/inet/hosts.

/etc/inet/hosts File Format

The /etc/inet/hosts file uses this basic syntax: (Refer to the hosts(4) man page for complete syntax information.)

IP-address hostname [nicknames] [#comment]

IP-address contains the IP address for each interface that the local host must know about.

hostname contains the host name assigned to the machine at setup, plus the host names assigned to additional network interfaces that the local host must know about.

[nickname] is an optional field containing a nickname for the host.

[# comment] is an optional field where you can include a comment.

Initial /etc/inet/hosts File

When you run the Solaris installation program on a machine, it sets up the initial /etc/inet/hosts file. This file contains the minimum entries that the local host requires: its loopback address, its IP address, and its host name.

For example, the Solaris installation program might create the following /etc/inet/hosts file for machine ahaggar shown in Figure 4-1:

Example 4-1 /etc/inet/hosts File for Machine ahaggar

127.0.0.1     localhost         loghost    #loopback address
192.9.200.3   ahaggar                      #host name

Loopback Address

In Example 4-1, the IP address 127.0.0.1 is the loopback address, the reserved network interface used by the local machine to allow interprocess communication so that it sends packets to itself. The ifconfig command uses the loopback address for configuration and testing, as explained in "ifconfig Command". Every machine on a TCP/IP network must use the IP address 127.0.0.1 for the local host.

Host Name

The IP address 192.9.200.3 and the name ahaggar are the address and host name of the local machine. They are assigned to the machine's primary network interface.

Multiple Network Interfaces

Some machines have more than one network interface, either because they are routers or multihomed hosts. Each additional network interface attached to the machine requires its own IP address and associated name. When you configure a router or multihomed host, you must manually add this information to the router's /etc/inet/hosts file. (See Chapter 5, Configuring Routers, for more information on setting up routers and multihomed hosts.)

Example 4-2 is the /etc/inet/hosts file for machine timbuktu shown in Figure 4-1.

Example 4-2 /etc/inet/hosts File for Machine timbuktu

127.0.0.1      localhost     loghost
192.9.200.70   timbuktu      #This is the local host name
192.9.201.10   timbuktu-201	#Interface to network 192.9.201

With these two interfaces, timbuktu connects networks 192.9.200 and 192.9.201 as a router.

How Name Services Affect the hosts Database

The NIS, NIS+, and DNS name services maintain host names and addresses on one or more servers. These servers maintain hosts databases containing information for every host and router (if applicable) on the servers' network. Refer to the Solaris Naming Administration Guide for more information about these services.

When Local Files Provide Name Service

On a network using local files for name service, machines running in local files mode consult their individual /etc/inet/hosts files for IP addresses and host names of other machines on the network. Therefore, their /etc/inet/hosts files must contain the:

• Loopback address

• IP address and host name of the local machine (primary network interface)

• IP address and host name of additional network interfaces attached to this machine, if applicable

• IP addresses and host names of all hosts on the local network

• IP addresses and host names of any routers this machine must know about, if applicable

• IP address of any machine your machine wants to refer to by its host name

Example 4-3 shows the /etc/inet/hosts file for machine tenere, a machine that runs in local files mode. Notice that the file contains the IP addresses and host names for every machine on the 192.9.200 network. It also contains the IP address and interface name timbuktu-201, which connects the 192.9.200 network to the 192.9.201 network.

A machine configured as a network client uses the local /etc/inet/hosts file for its loopback address and IP address.

Example 4-3 /etc/inet/hosts File for Machine Running in Local Files Mode