Two-Minute Drill

Here are some of the key points from the certification objectives in Chapter 13.

The Extended Internet Services Daemon (xinetd)

❑	xinetd acts as a "super-server" for a number of other network services, such as the Kerberos secured versions of Telnet and rsync.
❑	Individual services have their own management scripts in the /etc/xinetd.d directory.
❑	Most xinetd services are disabled by default.
❑	You can activate an xinetd service with the appropriate chkconfig command or by directly editing its xinetd script.
❑	xinetd listens for connection requests from client applications.
❑	When xinetd receives a connection request, it starts the server associated with the TCP/IP port and then waits for other connection requests.

The Secure Shell Package

❑	The OpenSSH command utilities-sshd, ssh, ssh-keygen, ssh-add, and ssh-agent-provide secure remote services over any network connections.
❑	Encryption is based on private and public keys.
❑	Public keys are shared with others, so that they can communicate with you through SSH.
❑	As it is easy to decipher traffic, even passwords, from telnet, ftp, and the "r" commands, it is best to use SSH on any publicly accessible network.

Dynamic Host Configuration Protocol (DHCP)

❑	DHCP allows a client computer to obtain network information (such as an IP number) from a server.
❑	The BOOTP protocol allows a client computer to access a DHCP server on a remote network.
❑	DHCP servers are configured through /etc/dhcpd.conf.
❑	The DHCP server daemon is dhcpd; the DHCP client daemon is dhclient.

The Network Time Protocol (NTP)

❑	NTP servers can help synchronize the systems on a network.
❑	NTP clients can be configured with the Date/Time Configuration tool, which can be started with the system-config-date command. Alternatively, clients can also be configured in /etc/ntp.conf.
❑	NTP clients can be synchronized with Stratum Two servers with the permission of their administrators; one alternative is the Public Time Server project at pool.ntp.org.
❑	To configure an NTP client as a server, the /etc/ntp.conf file needs to be configured to allow access to the desired networks.