Linux Networking and Security

1. Linux Networking and Security Chapter 2

2. 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

3. 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

4. Understanding Networked Devices in Linux

5. Understanding Networked Devices in Linux • 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

6. Preparing to Configure Networking

7. 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

8. 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

9. Configuring Networking with Command-Line Utilities

10. 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

11. Configuring Networking with Command-Line Utilities

12. 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

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. Configuring Networking Using Graphical Tools

24. 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

25. Using Basic Networking Utilities

26. 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

27. 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

28. Troubleshooting Network Connections

29. 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

30. 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

31. 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

32. 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

33. 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