## 2.2. Overview of Networking

Networks connect computers so that the different systems can share information. For users and system administrators, Unix systems have traditionally provided a set of simple but valuable network services, which let you check whether systems are running, refer to files residing on remote systems, communicate via electronic mail, and so on.

For most commands to work over a network, each system must be continuously running a server process in the background, silently waiting to handle the user's request. This kind of process is called a daemon; common examples, on which you rely for the most basic functions of your Linux system, are named (which translates numeric IP addresses into the alphanumeric names that humans are so fond of), lpd (which sends documents to a printer, possibly over a network), and ftpd (which allows you to connect to another machine via ftp).

Most Unix networking commands are based on Internet protocols. These are standardized ways of communicating across a network on hierarchical layers. The protocols range from addressing and packet routing at a relatively low layer to finding users and executing user commands at a higher layer.

The basic user commands that most systems support over Internet protocols are generally called TCP/IP commands, named after the two most common protocols. You can use all of these commands to communicate with other Unix systems besides Linux systems. Many can also be used to communicate with non-Unix systems, because a wide variety of systems support TCP/IP.

This section also covers NFS and NIS, which allow for transparent file and information sharing across networks, and sendmail.

### 2.2.1. TCP/IP Administration

ftpd | Server for file transfers.
gated | Manage routing tables between networks.
host | Print host and zone information.
ifconfig | Configure network interface parameters.
named | Translate between domain names and IP addresses.
netstat | Print network status.
nslookup | Query domain name servers.
ping | Check that a remote host is online and responding.
pppd | Create PPP serial connection.
rdate | Notify time server that date has changed.
route | Manage routing tables.
routed | Dynamically keep routing tables up to date.
slattach | Attach serial lines as network interfaces.
telnetd | Server for Telnet sessions from remote hosts.
tftpd | Server for restricted set of file transfers.

### 2.2.2. NFS and NIS Administration

domainname | Set or display name of current NIS domain.
makedbm | Rebuild NIS databases.
portmap | DARPA port to RPC program number mapper.
rpcinfo | Report RPC information.
ypbind | Connect to NIS server.
ypcat | Print values in NIS database.
ypinit | Build new NIS databases.
ypmatch | Print value of one or more NIS keys.
yppasswd | Change user password in NIS database.
yppasswdd | Update NIS database in response to yppasswd.
yppoll | Determine version of NIS map at NIS server.
yppush | Propagate NIS map.
ypserv | NIS server daemon.
ypset | Point ypbind at a specific server.
ypwhich | Display name of NIS server or map master.
ypxfr | Transfer NIS database from server to local host.

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