Chapter 04 - Linux Networking and Security Chapter 4 1...

1
Linux Networking and
Security
Chapter 4

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Configuring Client Services

Configure “superservers” to handle multiple network
services

Set up administrative services like logging and printing

Use simple network information services like finger and
talk

Understand basic mailing list and news server
configurations

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The Superservers

Superservers listen on multiple network ports and start
the appropriate service when a client connection arrives
for that port.

xinetd is a superserver gaining popularity

It is a revised version of inetd that creates a more secure
environment
 Shipped with Red Hat Linux

xinetd is the most widely used superserver

Application level security is provided via TCP Wrappers - the
tcpd program

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TCP Wrappers

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TCP Wrappers

TCP Wrappers - tcpd - is an application-level access
control program
 TCP Wrappers is not a firewall and should be used with one if
Linux security issues exist

Configuration is done by two files: /etc/hosts.allow and
/etc/hosts.deny

Ensure proper and expected configuration by testing carefully
before relying on it

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TCP Wrappers

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Services Beyond the Superserver

Many services do not rely on superservers, they are
designed to run standalone
 Apache Web server is the best example of this
 Servers such as SMTP and FTP can be used in standalone
mode, or with inetd or xinetd
 FTP runs more efficiently in standalone mode if much FTP traffic
is expected

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Exploring Network Testing Services

There are 5 common testing services and they are used
via Telnet
 The echo service repeats back whatever you type showing that
a remote host is receiving typed data

The chargen service returns a character stream and continues
to until the session is ended

The discard service is like /dev/null

The time service returns a number corresponding to the current
time and closes the connection

The daytime service returns the current date/time in human-
readable form, then ends the session

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Using Administrative Services

Logging with logd

System logging can be done remotely using syslogd by enabling
another host to receive syslog messages across the network
and specifying a host in /etc/syslog.conf

Printing with lpd
 Linux can print across the network using lpd when printer
definitions that specify remote hosts cause a local copy of lpd to
contact lpd running on a remote host and forward the print job to
that host

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Using Administrative Services

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Using Administrative Services