Transcript Linux Networking and Security

Linux Networking and
Security
Chapter 2
1
Configuring Basic Networking





Describe how networking devices differ from other Linux
devices
Configure Linux networking using scripts and text-mode
utilities
Configure UNIX networking using popular graphic
utilities
Effectively use networking utilities to test a network and
troubleshoot network problems
Understand the IPX and AppleTalk protocols
2
Understanding Networked Devices
in Linux

Linux design is based on the concept of the computer as
a collection of devices



Devices are accessed via the /dev directory
A device driver is software that knows how to communicate with
the device
Linux networking devices differ from most other devices
in several ways:



They are installed in the Linux kernel
Networking in Linux is handled by the kernel
Can refer to software as well as hardware
3
Understanding Networked Devices
in Linux
4
Understanding Networked Devices
in Linux

Point-to-Point Protocol (PPP)



Serial Line Internet Protocol (SLIP)



Allows a host to tie directly to a single computer
Commonly used to connect a modem to an ISP
Transmits data over a serial port
Used with serial modems to connect to ISPs
Integrated Services Digital Network (ISDN)


A special type of telephone service
ISDN is less favored than DSL and cable modems
5
Preparing to Configure Networking
6
Preparing to Configure Networking

To create a networking device, add the appropriate
module to the Linux kernel




The module will locate the networking card and create the
appropriate device name
Networking device kernel modules are normally found in the
/lib/modules directory
Use the modprobe command to load the networking device
Use the lsmod command to list the modules loaded in your
kernel at that point
7
Configuring Networking with
Command-Line Utilities

Use the ifconfig command to set up and check status of
networking interfaces



Parameters: network interface and IP address
Without parameters: status of all configured network interfaces
on the system
Use the route command to view or configure routing
table within the Linux kernel

Without parameters: displays the kernel routing table
8
Configuring Networking with
Command-Line Utilities
9
Configuring Networking with
Command-Line Utilities

Use the arp command to display the arp cache, a
mapping of IP addresses to hardware addresses


Used mainly for troubleshooting network connectivity
Also allows the addition and deletion of entries in the arp table
10
Configuring Networking with
Command-Line Utilities
11
System Networking Scripts

Linux vendors have provided numerous scripts and
configuration files to make complex networking easier to
manage



Scripts follow the model used for most system services on UNIXbased computers
Scripts are found in the /etc/sysconfig/network-scripts
subdirectory
Configuration files are found in the /etc/sysconfig/networking
subdirectory
12
Configuring Networking Using
Graphical Tools
13
Configuring Networking Using
Graphical Tools
14
Configuring Networking Using
Graphical Tools
15
Configuring Networking Using
Graphical Tools
16
Configuring Networking Using
Graphical Tools
17
Configuring Networking Using
Graphical Tools
18
Configuring Networking Using
Graphical Tools
19
Configuring Networking Using
Graphical Tools
20
Configuring Networking Using
Graphical Tools
21
Configuring Networking Using
Graphical Tools
22
Configuring Networking Using
Graphical Tools
23
Using Basic Networking Utilities

The Telnet Remote Login Utility





A terminal-emulator program that allows remote login as if
present at the computer itself
Use with caution due to security risks
To use Telnet, there must be a Telnet client and a Telnet server
The Telnet command requires the host name or IP address to
which the connection will be made
Use ssh instead
24
Using Basic Networking Utilities
25
Using Basic Networking Utilities

Using ping for System Testing



Uses the ICMP echo command to check the status of a remote
host
It is common to use a series of ping commands to test
networking and determine where a problem occurs
The ping command has numerous command-line options that
allow the setting of parameters such as the number of packets to
send before automatically stopping, the time to wait between
packets and the size of the packets
26
Using Basic Networking Utilities

Using traceroute to Examine Routing Patterns



Tracks each router between you and a destination host, showing
where the packets are going and how long each hop takes
Traceroute relies on the ttl field and ICMP “packet timed out”
messages to move step-by-step through the Internet to reach the
host specified
Command-line options include setting the maximum number of
routers to try, limiting the time to wait for each response and
indicating that packets cannot be fragmented
27
Troubleshooting Network
Connections
28
Other Networking Protocols

IPX and Linux



Internetwork Packet Exchange (IPX) was designed by Novell,
Inc.
Was replaced by IP when the Internet became more popular in
the early 1990’s
Apple Networking and Linux


AppleTalk is the networking protocol used by Macintosh
computers
On Linux, install the Netatalk package to allow Macintosh
computers to recognize Linux
29
Chapter Summary




Linux networking devices are created directly in the Linux kernel
when a kernel module supporting a type of networking is loaded
Many types of networking are supported in Linux, though the
most widely used for standard LANs is Ethernet
The modprobe command is used to add a networking module to
the Linux kernel and the currently-loaded kernel modules are
listed using the lsmod command
The ifconfig command sets up a networking interface in the
Linux kernel of displays the current setup for all configured
interfaces
30
Chapter Summary




The route command establishes entries in the kernel IP routing
table or displays the current routing table entries
The arp command lets you view the hardware address entries in
the system’s ARP cache
A number of networking scripts are used to streamline the
configuration of Linux networking, making it more flexible and
robust
Networking configuration parameters are stored in files within
the /etc/sysconfig/network-scripts directory
31
Chapter Summary




IP aliasing occurs when multiple IP addresses are assigned to
the same physical network interface
Red Hat Linux includes a powerful Network Administration Tool;
Caldera uses the Webmin browser-based interface to configure
networking; SuSE uses YaST
Enabling IP forwarding allows Linux to move packets between
multiple network interfaces on the same host, effectively
permitting a system to act as a router
The telnet utility lets you connect to a remote host as if you were
sitting at that host
32
Chapter Summary




Ping is a utility that uses the ICMP echo command to check
whether a remote host is accessible and alive
The traceroute command displays each of the intervening
routers between your host and another host you wish to contact
IPX is a useful protocol that originated with Novell’s NetWare
operating system, but is not widely used
AppleTalk is supported in Linux via the Netatalk package, which
you can add to Linux so that a Macintosh computer can see and
access Linux resources
33