Linux Networking and Security

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Linux Networking and Security

Chapter 2

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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

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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

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Point-to-Point Protocol (PPP) Allows a host to tie directly to a single computer Commonly used to connect a modem to an ISP

Serial Line Internet Protocol (SLIP) 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

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Preparing to Configure Networking

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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

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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

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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

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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 UNIX-

based computers Scripts are found in the /etc/sysconfig/network-scripts

subdirectory Configuration files are found in the /etc/sysconfig/networking

subdirectory

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Configuring Networking Using Graphical Tools

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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

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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

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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

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Troubleshooting Network Connections

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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

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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

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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

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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

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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

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Linux Networking and Security