Determining Host Configuration Modes

One of your key functions as a network administrator is configuring TCP/IP to run on hosts and routers (if applicable). You can set up these machines to obtain configuration information from two sources: files on the local machine or files located on other machines on the network. Configuration information includes:

• Host name of a machine

• IP address of the machine

• Domain name to which the machine belongs

• Default router

• Netmask in use on the machine's network

A machine that obtains TCP/IP configuration information from local files is said to be operating in local files mode. A machine that obtains TCP/IP configuration information from a remote machine is said to be operating in network client mode.

Machines That Should Run in Local Files Mode

To run in local files mode, a machine must have local copies of the TCP/IP configuration files. These files are described in "TCP/IP Configuration Files". The machine should have its own disk, though this is not strictly necessary.

Most servers should run in local file mode. This requirement includes:

• Network configuration servers

• NFS servers

• Name servers supplying NIS, NIS+, or DNS services

• Mail servers

Additionally, routers should run in local files mode.

Machines that exclusively function as print servers do not need to run in local files mode. Whether individual hosts should run in local files mode depends on the size of your network.

If you are running a very small network, the amount of work involved in maintaining these files on individual hosts is manageable. If your network serves hundreds of hosts, the task becomes difficult, even with the network divided into a number of administrative subdomains. Thus, for large networks, using local files mode is usually less efficient. On the other hand, because routers and servers must be self-sufficient, they should be configured in local files mode.

Network Configuration Servers

Network configuration servers are the machines that supply the TCP/IP configuration information to hosts configured in network client mode. These servers support three booting protocols:

• RARP - Reverse Address Resolution Protocol (RARP) maps known Ethernet addresses (48 bits) to IP addresses (32 bits), the reverse of ARP. When you run RARP on a network configuration server, this enables hosts running in network client mode to obtain their IP addresses and TCP/IP configuration files from the server. The in.rarpd daemon enables RARP services. Refer to the in.rarpd(1M) man page for complete details.

• TFTP - Trivial File Transfer Protocol (TFTP) is an application that transfers files between remote machines. The in.tftpd daemon carries out TFTP services, enabling file transfer between network configuration servers and their network clients.

• bootparams - The bootparams protocol supplies parameters for booting that are required by diskless clients. The rpc.bootparamd daemon carries out these services.

Network configuration servers can also can function as NFS file servers.

If you are going to configure any hosts as network clients, then you must also configure at least one machine on your network as a network configuration server. If your network is subnetted, then you must have at least one network configuration server for each subnet with network clients.

Machines That Are Network Clients

Any host that gets its configuration information from a network configuration server is said to be "operating" in network client mode. Machines configured as network clients do not require local copies of the TCP/IP configuration files.

Network client mode greatly simplifies administration of large networks. It minimizes the number of configuration tasks that must be performed on individual hosts and assures that all machines on the network adhere to the same configuration standards.

You can configure network client mode on all types of computers, from fully standalone systems to diskless and dataless machines. Although it is possible to configure routers and servers in network client mode, local files mode is a better choice for these machines. Routers and servers should be as self-sufficient as possible.

Diskless Booting

Setting up systems for diskless booting is described in the System Administration Guide.

Mixed Configurations

Due to the flexibility of the system, configurations are not limited to either an all-local-hosts mode or an all-network-client mode. The configuration of routers and servers typifies this, in that routers and servers should always be configured in local mode. For hosts, you can use any combination of local and network client mode you want.

Sample Network

Figure 4-1 shows the hosts of a fictional network with the network number 192.9.200. The network includes one network configuration server, the machine sahara. It serves the diskless client ahaggar. Machines tenere and nubian have their own disks and run in local files mode. Machine faiyum also has a disk but operates in network client mode.

Finally, the machine timbuktu is configured as a router. It includes two network interfaces, one named timbuktu on network 192.9.200 and one named timbuktu-201 on network 192.9.201. Both networks are in the organizational domain deserts.worldwide.com. The domain uses local files as its name service.

Most examples in this chapter use the network shown in Figure 4-1 as their basis.

Figure 4-1 Hosts in a Sample Network