16 qlx02vinternet


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16 qlx02vinternet

  1. 1. Unit 16 Connecting to the Internet
  2. 2. Objectives_ After completing this unit, you should be able to: • Connect to the Internet using a regular modem and an ISDN adapter • Describe how to connect to the Internet when using a broadband connection (cable or xDSL) • Describe the security issues involved in connecting to the Internet •Apply reasonable security measures
  3. 3. Connecting to the Internet • Connecting to the Internet = Establishing a channel which allows you to send IP packets to your ISP and vice versa • Four most common connection types: • REGULAR MODEM CONNECTION • ISDN CONNECTION •CABLE MODEM CONNECTION • xDSL connection • Connection types differ in: •COST (ONE-TIME, FIXED AND VARIABLE) • Bandwidth, Latency • Availability • Additional features such as fixed IP addresses
  4. 4. Modem Connections • Use an analog telephone line to establish a digital data connection (MOdulation/DEModulation) • PPP is used for IP packet encapsulation between your PC and the ISPs router Linux workstation JJ ECFÇDOHRDTTU J POWER I* Built-in or external modem ISP router )! ECFCDARDTTTRAJÎJ) ISP MODEM Internet
  5. 5. Modem Connections in Linux • External modems have device names /DEV/TTYSN • COM1 = ttyS0, COM2 = ttyS1 • Internal modems usually emulate a serial port - nothing special • Winmodems require a software driver which is usually only available under Windows (with a few exceptions) •To setup connection, need to invoke pppd • BEST DONE USING A GRAPHICAL FRONTEND SUCH AS kppp RSSIKNNN Connect to: | IBM Learning Services J Login ID: |TUXL| Password: I-™ SHOW LOG WINDOW M Quit Setup Help Connect | | I
  6. 6. ISDN Principles • ISDN = Integrated Services Digital Network • Provides a 100% digital network • POPULAR IN EUROPE • Most popular variant for home use is ISDN-2 • 2 channels, 64 Kbps each • One ISDN-2 connection can have up to eight Multiple Subscriber Numbers (MSN)
  7. 7. ISDN in Linux • Linux implements pseudo-tty's which accept regular modem commands to set up ISDN connections •/DEV/TTYI0 through /dev/ttyI63 • Can be used just like a modem in your Internet dialer • Need a special AT command to configure MSN: AT&E0123456789 •Applications can also access the ISDN adapter directly • Requires an ISDN-capable dialer such as isdn-config •SUPPORTS CHANNEL BUNDLING • Automatically configures MSN • More documentation: • /usr/src/linux/Documentation B Red Hat ISDN conflg «A?DIAL | PROVIDER | ® Hardware ] AAbout | Active providers: Connect Hangup ISDN state: OFFLINE Stop Online since: 00:00:00 | 00:00:00 ~Q-| Help APPLY I
  8. 8. Cable Modems Principles • Cable modems use available, but unused frequency ranges in the cable TV network •Typical bandwidth: 30 Mbps shared
  9. 9. xDSL Principles • Generic name for utilizing additional bandwidth in "local loop" of telephone network •Various implementations: ADSL, HDSL, SDSL, ... • Bandwidth is dependent on implementation, phone line quality and distance • Connecting requires a splitter or filters, and an xDSL modem Linux workstation with built- in XDSL ethernet adapter SPLITTER local loop /
  10. 10. Cable and xDSL in Linux • Most cable and xDSL modems connect to your Linux PC via a small Ethernet network, and bridge/route traffic into the ISPs network • Other connection types are possible too, but less common: USB, serial, wireless (not covered here) • Configure your ethernet adapter as directed by the ISP •STATIC IP ADDRESS • DHCP
  11. 11. Internet Security Being connected to the Internet is a security risk •ESPECIALLY WITH AN "ALWAYS ON" CONNECTION (CABLE, xDSL...) • Every workstation needs basic security measures • GOOD PASSWORDS • No unneeded services running • LATEST VERSIONS OF ALL SERVICES THAT ARE RUNNING •To determine network services that are running: # NETSTAT -ANUTP •To disable unneeded services: # chkconfig <SERVICE> off Never start your browser as root! Never log in to your system as root (unless needed)!
  12. 12. Checkpoint T/F 1. Linux-based systems are more secure than Microsoft-based systems. You therefore don't have to worry about security when connecting to the Internet. 2. Which of the following connection methods generally does NOT involve PPP? a. Regular modems b. ISDN connections c. Cable or xDSL 3. What is the device name of serial port COM2?
  13. 13. Unit Summary •There are four ways of connecting to the Internet: • REGULAR MODEM • ISDN CONNECTIONS • Cable modems • xDSL • Regular modems and ISDN connections are best configured using kppp or other graphical dialers • Cable and xDSL connections are typically configured as regular ethernet cards •The best network security on a Linux workstation is not to run any network services at all