Linux+ Guide to Linux Certification, Third Edition. Chapter 12 Network Configuration

Transcription

1 Linux+ Guide to Linux Certification, Third Edition Chapter 12 Network Configuration

2 Objectives Describe the purpose and types of networks, protocols, and media access methods Explain the basic configuration of TCP/IP Configure a Network interface to use TCP/IP Configure a modem, ISDN, and DSL interface Linux+ Guide to Linux Certification, 3e 2

3 Objectives (continued) Describe the purpose of host names and how they are resolved to IP addresses Configure TCP/IP routing Identify common network services Use command-line and graphical utilities to perform remote administration Linux+ Guide to Linux Certification, 3e 3

4 Networks Network: two or more computers joined via media and able to exchange information Local area networks (LANs): connect computers within close proximity e.g., used to allow connection to shared resources Wide area networks (WANs): connect computers separated by large distances e.g., used to connect to Internet Service Provider Internet service provider (ISP): company providing Internet access Linux+ Guide to Linux Certification, 3e 4

5 Networks (continued) Routers: computers capable of transferring information between networks Protocol: set of rules for communication between networked computers Packets: packages of data formatted by a network protocol Packets can be recognized by routers and other network devices Linux+ Guide to Linux Certification, 3e 5

6 Networks (continued) Linux network protocols: TCP/IP (Transfer Control Protocol/Internet Protocol) UDP/IP (User Datagram Protocol/Internet Protocol) IPX/SPX (Internetwork Packet Exchange/Sequence Packet Exchange) AppleTalk DLC (Data Link Control) DECnet (Digital Equipment Corporation network) Linux+ Guide to Linux Certification, 3e 6

7 Networks (continued) Media access method: defines how networked computers share access to the physical medium Contained within the hardware on NIC or modem Ethernet: most common network media access method Ensures that packets are retransmitted onto the network if a network error occurs Token ring: popular media access method Controls which computer has the ability to transmit information Linux+ Guide to Linux Certification, 3e 7

8 The TCP/IP Protocol Set of protocols with two core components TCP: ensures that packets are assembled in the correct order, regardless of arrival order IP: responsible for labeling each packet with destination address Together, TCP and IP ensure that information packets travel across the network as quickly as possible without getting lost Linux+ Guide to Linux Certification, 3e 8

9 IPv4 Addresses IP address: unique number that identifies a networked computer Octet: series of four 8-bit numbers Common format of IPv4 addresses Unicast: directed TCP/IP communication from one computer to another single computer Linux+ Guide to Linux Certification, 3e 9

10 IPv4 Addresses (continued) IPv4 addresses composed of two parts Network ID: network on which a computer is located Host ID: single computer on that network Two computers with different network IDs can have the same host ID Only computers with same network ID can communicate without a router Linux+ Guide to Linux Certification, 3e 10

11 Subnet Masks Define which part of IP address is the network ID and which part is the host ID Series of four octets Octet in subnet mask containing 255 is part of network ID Octet in subnet mask containing 0 is part of host ID ANDing: calculate network and host IDs from an IP address and subnet mask Compare binary bits Linux+ Guide to Linux Certification, 3e 11

12 Subnet Masks (continued) Figure 12-1: A sample IP address and subnet mask Linux+ Guide to Linux Certification, 3e 12

13 Subnet Masks (continued) = all networks = all computers on all networks 255 in an IP address can specify many hosts Broadcast addresses Linux+ Guide to Linux Certification, 3e 13

14 Default Gateway IP address of network interface on a router, to which you send packets Routers can distinguish between different networks Move packets between them Have assigned IP addresses on each attached network Linux+ Guide to Linux Certification, 3e 14

15 IPv4 Classes and Subnetting IP address class defines default subnet mask of associated device All IP address classes can be identified by first octet Class A: 8 bits for network ID, 24 bits for host ID Assigned to very large companies Class B: 16 bits for network ID, 16 bits for host ID Assigned to larger organizations with several thousand users Class C: 24 bits for network ID, 16 bits for host ID Used for small and home networks Linux+ Guide to Linux Certification, 3e 15

16 IPv4 Classes and Subnetting Multicast: TCP/IP communication destined for a certain group of computers Class D addresses Subnetting: divide a large network into smaller networks Control traffic flow Take bits from host ID; give to network ID Linux+ Guide to Linux Certification, 3e 16

17 IPv4 Classes and Subnetting (continued) Table 12-1: IP address classes Linux+ Guide to Linux Certification, 3e 17

18 The IPv6 Protocol Number of IP addresses using IPv4 is unsuitable for Internet growth IPv6 protocol: uses 128 bits to identify computers Addresses written using eight 16-bit hexadecimal numbers IPv6 address contains two portions First half assigned by ISP and identifies network Last half is link local portion: used to uniquely identify computers in a LAN Linux+ Guide to Linux Certification, 3e 18

19 The IPv6 Protocol (continued) Few networks have adopted IPv6 Proxy servers and NAT routers: computers or hardware devices that have an IP address and access to a network Used by other computers to obtain network resources on their behalf Allows computers behind different NAT routers or proxy servers to have the same IPv4 address Linux+ Guide to Linux Certification, 3e 19

20 Configuring a Network Interface If NIC detected during installation, Fedora Linux automatically configures appropriate driver insmod and modprobe commands: used to load kernel objects into the Linux kernel Can be used to load NIC drivers lsmod command: displays a list of currently loaded modules rmmod command: removes module from kernel Most modules loaded from dist.conf file in the /etc/modprobe.d directory Linux+ Guide to Linux Certification, 3e 20

21 Configuring a Network Interface (continued) ifconfig command: assign TCP/IP configuration to a NIC Also used without any arguments to view configuration of all network interfaces in computer dhclient command: receive TCP/IP configuration from DHCP or Boot Protocol (BOOTP) server Automatic private IP addressing (APIPA): automatic assignment of IP address in the absence of BHCP and BOOTP Linux+ Guide to Linux Certification, 3e 21

22 Configuring a Network Interface (continued) /etc/sysconfig/network-scripts/ifcfg-interface file: Stores NIC configurations Allows the system to activate and configure TCP/IP information at each boot time ifdown command: unconfigures a NIC ifup command: configures NIC using /etc/sysconfig/network-scripts/ifcfg-interface file ping (Packet Internet Groper) command: Check TCP/IP connectivity on a network -c option: limit the number of ping packets sent Linux+ Guide to Linux Certification, 3e 22

23 Configuring a Network Interface (continued) Figure 12-2: Configuring network interfaces Linux+ Guide to Linux Certification, 3e 23

24 Configuring a Network Interface (continued) Figure 12-3: Configuring TCP/IP information for a network interface Linux+ Guide to Linux Certification, 3e 24

25 Configuring a Network Interface (continued) Mobile commuters typically connect to many different NICs, both wired and wireless Network Manager daemon: allows users to quickly connect to wired and wireless networks from desktop environments Linux+ Guide to Linux Certification, 3e 25

26 Configuring a PPP Interface Run TCP/IP over serial lines using a WAN protocol Three common Point-to-Point Protocol (PPP) connection technologies: Modems ISDN DSL Linux+ Guide to Linux Certification, 3e 26

27 Configuring a PPP Interface (continued) Modems: send TCP/IP information across normal telephone lines Considered slow Transmit information on a serial port ISDN: set of standards designed to transmit data over copper telephone lines DSL: connects to Ethernet NIC and transmits data across normal telephone lines Linux+ Guide to Linux Certification, 3e 27

28 Configuring a PPP Interface (continued) Normally configured manually after Linux installation is complete Requires: Support for PPP compiled into kernel PPP daemon Supporting utilities such as chat program Can use graphical programs to configure files and utilities to allow PPP communication Linux+ Guide to Linux Certification, 3e 28

29 Configuring a PPP Interface (continued) Figure 12-5: Adding a network interface Linux+ Guide to Linux Certification, 3e 29

30 Configuring a PPP Interface (continued) Information about PPP devices stored in files named ifcfg-internetserviceprovidername Located in /etc/sysconfig/network-scripts directory Other configurations used by PPP daemon stored in /etc/ppp and /etc/isdn directories Incorrect passwords are the most common problem with PPP connections Need to activate PPP device after configuration Linux+ Guide to Linux Certification, 3e 30

31 Name Resolution Hostnames: user-friendly computer name Fully qualified domain name (FQDN): hostname following DNS convention DNS: hierarchical namespace for host names whois command: used to obtain registration information about a domain within a name space hostname command: view or set a computer s host name Linux+ Guide to Linux Certification, 3e 31

32 Name Resolution (continued) Figure 12-6: The domain name space Linux+ Guide to Linux Certification, 3e 32

33 Name Resolution (continued) TCP/IP cannot identify computers via hostnames Must map hostnames to IP addresses Can be done by placing entries in the /etc/hosts file ISPs list FQDNs in DNS servers on Internet Applications request IP addresses associated with a specific FQDN Configure by specifying the IP address of the DNS server in /etc/resolv.conf file Linux+ Guide to Linux Certification, 3e 33

34 Routing Route table: list of TCP/IP networks stored in system memory route command: displays the route table Multihomed hosts: computers with multiple network interfaces IP forwarding: forwarding packets from one interface to another Also known as routing Linux+ Guide to Linux Certification, 3e 34

35 Routing (continued) Enabling routing: Place number 1 in: /proc/sys/net/ipv4/ip_forward for IPv4 /proc/sys/net/ipv6/conf/all/forwarding for IPv6 To enable routing at every boot: Edit the /etc/sysctl.conf file to include: net.ipv4.ip_forward = 1 for IPv4 net.ipv6.conf.default.forwarding = 1 for IPv6 Linux+ Guide to Linux Certification, 3e 35

36 Routing (continued) Large networks may have several routers Packet may travel through several routers May require adding entries in the router table route add <route> command: add entries to route table route del <route> command: remove entries from route table ip command: can be used to manipulate the route table Linux+ Guide to Linux Certification, 3e 36

37 Routing (continued) Figure 12-7: A sample routed network Linux+ Guide to Linux Certification, 3e 37

38 Routing (continued) Contents of route table lost when computer powered off Add to /etc/rc.d/rc.local file Most routers configured with a default gateway For packets addressed to destinations not in route table traceroute command: troubleshoot routing Displays routers between current and remote computer Linux+ Guide to Linux Certification, 3e 38

39 Network Services Must identify types and features of network services before they can be configured Network services: processes that provide some type of valuable service for client computers on network Often presented by daemon processes that listen to certain requests Daemons identify packets to which they should respond using a port number Linux+ Guide to Linux Certification, 3e 39

40 Network Services (continued) Port: number uniquely identifying a network service Ensure that packets delivered to proper service Range from 0 to /etc/services file: lists ports and associated protocol Well-known port: ports from 0 to 1023 Represent commonly used services Linux+ Guide to Linux Certification, 3e 40

41 Network Services (continued) Table 12-2: Common well-known ports Linux+ Guide to Linux Certification, 3e 41

42 Network Services (continued) Internet super daemon (xinetd): initializes appropriate daemon to provide needed network service Stand-alone daemons: daemons that provide network services directly Log information themselves to subdirectories under /var/log chkconfig command or ntsysv utility can be used to configure most stand-alone daemons to start in various runlevels Linux+ Guide to Linux Certification, 3e 42

43 Network Services (continued) Figure 12-8: Interacting with network services Linux+ Guide to Linux Certification, 3e 43

44 Network Services (continued) Table 12-3: Common network services Linux+ Guide to Linux Certification, 3e 44

45 Network Services (continued) Table 12-3 (continued): Common network services Linux+ Guide to Linux Certification, 3e 45

46 Network Services (continued) Table 12-3 (continued): Common network services Linux+ Guide to Linux Certification, 3e 46

47 Network Services (continued) Table 12-3 (continued): Common network services Linux+ Guide to Linux Certification, 3e 47

48 Remote Administration: Telnet telnet command: traditionally used to obtain a command-line shell on remote server Receives host name or IP address of remote computer as argument Easiest way to perform remote administration Need to install telnet daemon using yum command Use regular commands and exit to kill remote BASH shell Linux+ Guide to Linux Certification, 3e 48

49 Remote Commands Remote commands: set of commands that can be used to execute commands on remote systems yum install rsh-server rlogin command: obtains a shell from remote computer on network rcp command: copies files between computers rsh command: used to execute a command on a remote computer Linux+ Guide to Linux Certification, 3e 49

50 Remote Commands (continued) r commands allow access to remote computers without a password, if remote computer has trusted access Trusted access: computers allowed to access a computer without providing a password Does not apply to root user Methods of setting up: Add host names of computers to /etc/hosts.equiv Create and.rhosts file in the home directory of each user who should get trusted access Linux+ Guide to Linux Certification, 3e 50

51 Secure Shell (SSH) Secure Shell (SSH): encrypts information passing between computers Secure replacement for r commands ssh command: connects to a remote computer running ssh daemon Receives host name or IP address of target computer as argument Accept RSA encryption fingerprint for target computer Can be used to transfer files between computers Linux+ Guide to Linux Certification, 3e 51

52 Secure Shell (SSH) (continued) Main types of encryption supported by ssh daemon: Triple Data Encryption Standard (3DES) Advanced Encryption Standard (AES) Blowfish Carlisle Adams Stafford Tavares (CAST) ARCfour Linux+ Guide to Linux Certification, 3e 52

53 Remote X Windows X Windows is a network application Can be used to obtain graphical utilities from remote Linux computer To obtain graphical utilities using X Windows: Edit /etc/gdm/custom.conf Use xhost + command within a graphical terminal to allow other computers to write X Windows clients on your computer Connect to remote computer with telnet or ssh, and export DISPLAY variable of the local computer Linux+ Guide to Linux Certification, 3e 53

54 Virtual Network Computing (VNC) Graphical option for administering Linux remotely Other computers run VNC client that connects to VNC server daemon installed on local computer to obtain a desktop environment Remote FrameBuffer (RFB): platform-independent protocol used to transfer graphics, mouse movements and keystrokes across network vncpasswd command: used to configure password for VNC connection vncviewer command: connects to VNC server Linux+ Guide to Linux Certification, 3e 54

55 Summary A network is a collection of connected computers that share information A protocol is a set of rules that defines the format of information that is transmitted across a network Each computer on a TCP/IP network must have a valid IPv4 or IPv6 address The IPv4 configuration of a network interface can be specified manually, obtained automatically from a DHCP or BOOTP server, or autoconfigured by the system Linux+ Guide to Linux Certification, 3e 55

56 Summary (continued) The IPv6 configuration of a network interface can be obtained from a router using ICMPv6, from a DHCP server, or autoconfigured by the system The /etc/sysconfig/network-scripts directory contains the configuration for NIC and PPP interfaces Host names are computer names that are easy for humans to remember; host names that follow the DNS are FQDNs Host names must be resolved to an IP address before network communication can take place Linux+ Guide to Linux Certification, 3e 56

57 Summary (continued) Routers are devices that forward TCP/IP packets from one network to another; each computer and router has a route table used to determine how TCP/IP packets are forwarded Network services are started by the Internet Super Daemon or by stand-alone daemons There are many ways to remotely administer a Linux system, including the telnet, rsh, rcp, rlogin, and ssh commands, X Windows and VNC Linux+ Guide to Linux Certification, 3e 57