A Solaris network consists of a number of different hosts that are interconnected using a switch or a hub. Solaris networks connect to one another via routers, which can be dedicated hardware systems, or Solaris systems, which have more than one network interface. Each host on a Solaris network is identified by a unique hostname; these hostnames often reflect the function of the host in question. For example, a set of four FTP servers may have the hostnames ftp1, ftp2, ftp3, and ftp4.
Every host and network that is connected to the Internet uses the Internet Protocol (IP) to support higher-level protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Every interface of every host on the Internet has a unique IP address that is based on the network IP address block assigned to the local network. Networks are addressable by using an appropriate netmask that corresponds to a class A (255.0.0.0), class B (255.255.0.0), or class C (255.255.255.0) network.
Solaris supports multiple Ethernet interfaces that can be installed on a single machine. These are usually designated as /etc/hostname.hmen, where n is the interface number and hme is the interface type. Interface files contain a single unqualified domain name or IP address, with the primary network interface being designated with an interface number of zero. Thus, the primary interface of a machine called ftp would be defined by the file /etc/hostname.hme0, which might contain the unqualified domain name “ftp”, or the IP address 126.96.36.199. A secondary network interface, connected to a different subnet, might be defined in the file /etc/hostname.hme1. In this case, the file might contain the unqualified domain name “mail”, or the IP address 10.17.65.28.
The decision to use unqualified domain names or IP addresses rests largely with the naming service used by the system, which is defined by the file /etc/nsswitch.conf. If this file does not allow hostname resolution from the /etc/hosts because the Domain Name System (DNS) is used exclusively, using unqualified domain names in /etc/hostname.* files can lead to a failure of local hostname resolution. However, because IP addresses can change from time to time (particularly if Dynamic Host Configuration Protocol, or DHCP, is used), some administrators may need to use unqualified domain names.
Enabling multiple interfaces is commonly used in organizations that have a provision for a failure of the primary network interface or to enable load balancing of server requests across multiple subnets (for example, for an intranet web server processing HTTP requests). A system with a second network interface can act either as a router or as a multihomed host. Hostnames and IP addresses are locally administered through a naming service, which is usually DNS for companies connected to the Internet, and the Network Information Service (NIS/NIS+) for companies with large internal networks that require administrative functions beyond what DNS provides, including centralized authentication.
It is also worth mentioning at this point that it is possible for you to assign different IP addresses to the same network interface; this configuration can be useful for hosting “virtual” interfaces that require their own IP address, rather than relying on application-level support for multihoming (for example, when using the Apache web server). You simply create a new /etc/hostname.hmeX:Y file for each IP address required, where X represents the physical device interface and Y represents the virtual interface number.
The subnet mask used by each of these interfaces must also be defined in /etc/ netmasks. This is particularly important if the interfaces lie on different subnets, or if they serve different network classes. In addition, it might also be appropriate to assign a fully qualified domain name to each of the interfaces, although this will depend on the purpose to which each interface is assigned.