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Chapter 12: Configuring Networks

Chapter 12: Configuring Networks. The Complete Guide to Linux System Administration. Objectives. Configure network interfaces using command-line and graphical utilities Set up a simple DHCP server Manage networked printing services. Configuring Linux Networking. Learn more about

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Chapter 12: Configuring Networks

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  1. Chapter 12:Configuring Networks The Complete Guide to Linux System Administration

  2. Objectives • Configure network interfaces using command-line and graphical utilities • Set up a simple DHCP server • Manage networked printing services The Complete Guide to Linux System Administration

  3. Configuring Linux Networking • Learn more about • Networking protocols • Network configuration The Complete Guide to Linux System Administration

  4. Understanding Network Devices in Linux • Linux networking devices • Not shown in /dev directory • Do not “exist” on system until appropriate device driver installed in kernel • Networking device • Named channel over which network traffic can pass • Device drivers for networking are kernel modules The Complete Guide to Linux System Administration

  5. Understanding Network Devices in Linux (continued) • Kernel modules can be loaded or unloaded while Linux is running • /dev/eth0 • First Ethernet card installed on system • Media Access Control (MAC) address • Unique address assigned by Ethernet card manufacturer The Complete Guide to Linux System Administration

  6. Understanding Network Devices in Linux (continued) • To obtain MAC address • Host broadcasts message to entire network segment using Address Resolution Protocol (ARP) • Host with IP address responds directly to computer that sent ARP request with MAC address • Source host stores MAC address and IP address The Complete Guide to Linux System Administration

  7. Understanding Network Devices in Linux (continued) • arp command • Display ARP cache • Mapping of IP addresses to hardware addresses • Used mainly for troubleshooting network connectivity • Refreshed frequently The Complete Guide to Linux System Administration

  8. Configuring Networking with Command-line Utilities • ifconfig command • Set up network configuration in Linux kernel • Parameters include: • Network interface • IP address assigned to interface • Network mask • Syntax • ifconfig device ip_address netmask address broadcast address The Complete Guide to Linux System Administration

  9. Configuring Networking with Command-line Utilities (continued) • Packet • Unit of data that network card transmits • Broadcast address sends packet to all computers on same part of network • Maximum transmission unit (MTU) • Maximum size of packet interface supports The Complete Guide to Linux System Administration

  10. Configuring Networking with Command-line Utilities (continued) • View status of interface: ifconfig eth0 • Stop Ethernet interface: ifconfig eth0 down • Start Ethernet interface: ifconfig eth0 up • Routing table tells networking software where to send packets that are not part of local network The Complete Guide to Linux System Administration

  11. Configuring Networking with Command-line Utilities (continued) • route command • View or configure routing table within kernel • Executed at boot time when networking initialized • Output information for addresses • 192.168.100.0 (eth0 IP address) • 127.0.0.0 • Other The Complete Guide to Linux System Administration

  12. Configuring Networking with Command-line Utilities (continued) • Route command output • Destination – Ref • Gateway – Use • Genmask – Iface • Flags • Add route example: • route add -net 192.168.100.0 netmask 255.255.255.0 dev eth0 The Complete Guide to Linux System Administration

  13. Configuring Networking with Command-line Utilities (continued) • service command • Start or stop networking • Relies on script /etc/rc.d/init.d/network • /etc/sysconfig/networking/devices configuration directory • Contains file for each network device • ifcfg-eth0 file • Used by /etc/rc.d/init.d/network script • As it executes ifconfig and route commands The Complete Guide to Linux System Administration

  14. Configuring Networking with Command-line Utilities (continued) • ifup and ifdown scripts manage single interface, rather than all network interfaces • Better than using ifconfig command directly • Looks at parameters and associated functionality needed to cleanly manage interface • Example: ./ifdown eth0 • Some systems have two or more physical network devices The Complete Guide to Linux System Administration

  15. Configuring Networking with Command-line Utilities (continued) • IP forwarding • Allows packets to be passed between network interfaces • Required for any router • To enable: echo 1 > /proc/sys/net/ipv4/ip_forward • Linux includes graphical utilities that set up and manage networking The Complete Guide to Linux System Administration

  16. Configuring Networking Using Graphical Tools • system-config-network program • Included with Red Hat Linux and Fedora • Devices tab • List of each Linux networking device • Name and type of hardware driver The Complete Guide to Linux System Administration

  17. Configuring Networking Using Graphical Tools (continued) The Complete Guide to Linux System Administration

  18. Configuring the DNS Resolver • DNS • Used to convert host and domain names into IP addresses • Implemented by server that supports DNS • Reverse DNS converts IP address to domain name • Resolving • Process of converting domain name to IP address or vice versa The Complete Guide to Linux System Administration

  19. Configuring the DNS Resolver (continued) • Resolver • Client part of DNS • Makes requests to DNS server • Test by pinging another system using host name instead of IP address • Configured by file /etc/resolv.conf • Contains IP address of one or more DNS servers preceded by keyword nameserver • Can include up to three DNS servers The Complete Guide to Linux System Administration

  20. Configuring the DNS Resolver (continued) • Keyword • Word to which program reading configuration file attaches special meaning • Utilities for researching DNS problems: • dnsquery – whois • nslookup – host • dig • /etc/hosts file stores IP addresses and corresponding domain names in text file on host The Complete Guide to Linux System Administration

  21. Configuring the DNS Resolver (continued) • /etc/hosts file • By default contains only host name localhost and own host’s name • On small network: • Create hosts file that contains each host and IP address of host • Avoid need for DNS server • Can have nonlocal domain names resolved by request to DNS server • Configuring DNS resolver graphically uses system-config-network to set up resolver The Complete Guide to Linux System Administration

  22. Configuring the DNS Resolver (continued) The Complete Guide to Linux System Administration

  23. Dynamic Routing with Routing Protocols • Static routing • Uses preconfigured routing table • Not good choice for: • Larger networks • Unreliable connections • Dynamic routing uses specialized routing protocol to build and modify routing tables automatically The Complete Guide to Linux System Administration

  24. Dynamic Routing with Routing Protocols (continued) The Complete Guide to Linux System Administration

  25. Dynamic Routing with Routing Protocols (continued) • Routing protocols divided into two categories • Interior: designed for routing packets among networks under your control • Exterior: designed for routing packets between networks controlled by different organizations • All routing protocols designed to exchange information among routers The Complete Guide to Linux System Administration

  26. Dynamic Routing with Routing Protocols (continued) • Routing Information Protocol (RIP) • Interior routing protocol • Oldest routing protocol still in common use • Implemented in Linux using routed daemon • Easy to configure and run • Choice of most network administrators The Complete Guide to Linux System Administration

  27. Dynamic Routing with Routing Protocols (continued) • Open Shortest Path First (OSPF) protocol • Interior routing protocol • Designed to work effectively even in very large networks • Uses technique called flooding • Few Linux network administrators use it • Implemented using gated daemon The Complete Guide to Linux System Administration

  28. Dynamic Routing with Routing Protocols (continued) • Border Gateway Protocol (BGP) • Designed for routing between major national networks • Supported by gated daemon The Complete Guide to Linux System Administration

  29. Configuring a DHCP Server • DHCP server installed by default on many Linux systems • /etc/dhcpd.conf file • Configuration for DHCP • Instructs DHCP server which IP address ranges are available for DHCP clients The Complete Guide to Linux System Administration

  30. Configuring a DHCP Server (continued) • When client requests IP address : • DHCP server leases address to client for specified time • At end of lease client must request new IP address • Whole arrangement transparent to user on client host • DHCP client can run on any operating system The Complete Guide to Linux System Administration

  31. Networked Printing Services • Linux includes network printing capabilities The Complete Guide to Linux System Administration

  32. Using Traditional Linux Printing: LPRng • Traditional Linux printing system • Based on BSD version of UNIX • Allows multiple users to print files at same time to: • Local printer • Networked printers • Print queues • System administrator must define printers • Printer definitions describe type of printer and features to be used The Complete Guide to Linux System Administration

  33. Using Traditional Linux Printing: LPRng (continued) • Printing file in LPRng system • Application submits file to be printed (print job) • Print job processed by print filter converts information from Linux application into formatting codes to produce desired output • Printing utility stores print job in print spool directory • Default directory /var/spool/lpd • Lpd print server program keeps track of all print jobs in all print queues on system The Complete Guide to Linux System Administration

  34. Using Traditional Linux Printing: LPRng (continued) • Correlation between print queue and physical printer not always one to one • Linux print filter • Same as printer driver in other operating systems • Converts documents or images into format that printer can use The Complete Guide to Linux System Administration

  35. Using Traditional Linux Printing: LPRng (continued) The Complete Guide to Linux System Administration

  36. Using Traditional Linux Printing: LPRng (continued) • Page description language • Special set of codes • Determine graphic elements, text font, and everything else about what appears on printed page • Most widely used: • PostScript • Printer Control Language (PCL) The Complete Guide to Linux System Administration

  37. Using Traditional Linux Printing: LPRng (continued) • Magic filter • Can convert documents for many different printers • Convenient to support hundreds of printers • Doesn’t allow Linux to use specialized features of each printer • Script /usr/share/printconf/util/mf_wrapper • Main print filter in Red Hat Linux and Fedora • Starts magicfilter-t program • Uses several other programs in conversion process The Complete Guide to Linux System Administration

  38. Using Traditional Linux Printing: LPRng (continued) • Configuring local printer definitions • Each LPRng printer definition created as print queue entry in /etc/printcap configuration file • Uses complex format • Must provide appropriate Linux device name • Parallel ports use device name lp followed by device number • Serial ports use name ttyS followed by device number The Complete Guide to Linux System Administration

  39. Printing Remotely Using LPRng • Define printer on system that refers to remote computer and print queue on remote system • Key options in configuration file • rm remote system specified • rp remote print queue specified • Once print job has been sent to remote system using lpd, user has no direct control over it The Complete Guide to Linux System Administration

  40. Printing Remotely Using LPRng (continued) The Complete Guide to Linux System Administration

  41. Understanding the Common UNIX Printing System (CUPS) • Provides new architecture for Linux printing • Users browse network to find and print to networked printers and other devices • System administrators manage printer definitions and print jobs across network • Installed by default in Red Hat Linux and Fedora • cupsd • Main print server daemon The Complete Guide to Linux System Administration

  42. Understanding the Common UNIX Printing System (CUPS) (continued) • cupsd print server daemon • Uses HTTP protocol • Manages printers using web browser interface • CUPS architecture uses network port 631 • Start CUPS user interface • http//localhost:631/ • /etc/cups/cupsd.conf file specifies setting for each active server option The Complete Guide to Linux System Administration

  43. Understanding the Common UNIX Printing System (CUPS) (continued) The Complete Guide to Linux System Administration

  44. Understanding the Common UNIX Printing System (CUPS) (continued) • Many printers are configured using PostScript Printer Description (PPD) file • Manufacturers can easily create text-based configuration file • Permits printer to be graphically configured using standard utilities • CUPS class • Group of printers to which user can submit print job • First available printer within used to print job The Complete Guide to Linux System Administration

  45. Managing Printing • Printing policy • Brief statement of rules describing: • How printing resources can be used • How printers should be managed • lpc utility controls LPRng or CUPS printing • Alternatives printing system • Maps print command to different programs • Based on which printing system in use The Complete Guide to Linux System Administration

  46. Managing Printing (continued) • Alternatives command • lpr command and lpc command • Symbolic links • Using lpc • Prevent new print jobs from being accepted by print queue • Prevent print jobs from being sent to printer • Cancel print job currently being printed • See status of any printer The Complete Guide to Linux System Administration

  47. Managing Printing (continued) • lpq utility lists each print job in print queue with status information • lprm command deletes print job from queue • Graphical print management utilities • Print Manager The Complete Guide to Linux System Administration

  48. Summary • Ethernet card includes unique MAC address • Used by address resolution protocol • ifconfig command used to configure networking interface in kernel • route command modifies internal routing table • system-config-network utility graphically configures network devices The Complete Guide to Linux System Administration

  49. Summary (continued) • DHCP server on Linux requires configuring /etc/dhcpd.conf file • Linux printing relies on printer definitions • Red Hat Linux and Fedora support both LPRng and CUPS printing using alternatives printing system • Print jobs can be managed using command line utilities or graphical interface The Complete Guide to Linux System Administration

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