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.SLIP lacks any error detection, whereas PPP implements it.Given the choice, PPP is the better serial-line TCP protocol, although it is not available with all operating system implementations.SLIP and PPP connections are usually established in the same manner as the Ethernet drivers.SCO UNIX, for example, uses the netconfig utility, mentioned previously.When adding a SLIP or PPP chain, the system prompts for the serial line to be used, the baud rate, the address of the local and destination machines, and the remote machine's name.It then configures the system to use that serial port.After relinking the kernel and rebooting, the serial line is available for either SLIP or PPP (depending on the way it was configured).Remote PrintingRemote printing is a useful feature that enables a user on one machine to send print jobs to other machines that have attached printers.The system is called Remote Line Printing (RLP) and is commonly used to share printers in a workgroup.It is also useful for enabling access to specialty printers such as color lasers and plotters.RLP does not support printer classes, and some operating systems impose restrictions on supported print command-line options.Remote administration of printers is not supported.RLP functions differently than normal UNIX printing.When a print request is issued, the system consults the printer configuration file (usually /etc/printcap) to determine if the printer is local or remote.If the print request is for a local printer, the usual process applies.If the request is for a remote printer, the local system spools the print request and invokes the lpd daemon, which packages the print request and sends it to the remote machine, where it is spooled for the printer.A user can set a remote printer as the default destination, as is commonly done in workgroups that share a single printer.Several versions of RLP are available with support for different operating systems on a network.SCO UNIX, for example, supports two kinds of clients: SCO-based systems and 4.3BSD systems.This enables workstations running Berkeley's 4.3BSD to queue print requests to SCO print servers.SCO clients use RLP with the same commands as a local printer would (lp and cancel), but 4.3BSD clients have special versions of the commands (lpr and lprm).Assuming that RLP is available with your operating system (some versions of UNIX do not support it), it is usually installed and activated with a script or utility program.With SCO UNIX, a mkdev rlp command initiates the installation script.Other operating systems use a similar utility.During the installation process, a number of directories are created to handle the spooling, and modifications are made to the printer configuration files.The old printing commands are archived to a directory, and new versions that support RLP are copied into their place.Remote printing requires a special entry in the printer configuration file (/etc/printcap).Some operating systems (such as SCO UNIX) have a script that edits the file for you, prompting for the configuration information.A sample line in the file for a remote printer would look like this:hplaser::lp=:rm=main_hplaser:rp=hplaser:sd=/usr/spool/lpd/hplaserThe first field is the name used by the local machine to refer to the printer.The second field is usually empty.It defines the name of an error log file but is not used on most systems.The third field is the device name for a local printer.Remote printers leave the field as lp= with no specified printer.The fourth field is the network name for the printer.It can be the same as the local name.The fifth field is the name the print server uses for the printer (usually the same as the local name).Finally, the sixth field is the name of the spooling directory for the printer.This is where print requests are spooled before being sent to the remote printer.In order for machines on the network to access the Hewlett-Packard LaserJet that is attached to the main machine on the sample network, the three remote machines should have entries for the printer in their /etc/printcap files.The main machine also has an entry for it, but as a local printer.Administering a remote printer is done either by logging into the console of the machine to which the printer is attached or by using several RLP utilities from another machine.The utilities differ with each operating system.Windows NT Server has remote TCP/IP printing capabilities available as part of the TCP/IP suite.Configuring SNMPMost TCP/IP networks use the Simple Network Management Protocol (SNMP) to monitor the network for problems.It enables a system to examine and alter networking information maintained by other machines on the network.SNMP is a simple protocol that uses UDP as a transport.Many UNIX operating systems use a daemon to run SNMP [ Pobierz całość w formacie PDF ]
