Chapter 6: Internet Infrastructure

1
Chapter 6 Internet Infrastructure

• i-Net Guide to the Internet
• Third Edition

2
Objectives

• Learn how networks are segmented to improve
  performance and how hardware devices work to
  segment a network
• Investigate the way large networks are divided
  logically into subnets to make them easier to
  manage and improve performance
• Study data routing across the Internet

3
Objectives (Continued)

• Learn how domain names are used and managed on
  the Internet
• Learn how servers and Internet security
  appliances can be used to enable and improve the
  performance and reliability of a network and the
  Internet
• Compare bandwidth technologies used on LANs, WAN,
  and the Internet

4
Physically and Logically Dividing a Large Network

• You can divide a network using two approaches
• You can physically divide the network using
  hardware devices
• You can logically divide the network using
  software settings
• The first approach is called segmenting the
  network the second approach is called
  subnetting.

5
Bridges and Switches

• Bridges and switches are more intelligent than
  hubs and make decisions involving whether to
  allow traffic to pass or where to route that
  traffic, reducing traffic on each segment and
  improving network performance.
• A routing table is a database stored within a
  router that is used to find the best network path
  on which to forward information.
• A network bridge keeps routing tables for each
  network to which it connects.

6
Bridges and Switches (Continued)

• The tables start out empty and all data packets
  that reach the bridge from one segment are passed
  on to the other segment connected to the bridge.
• Just like bridges, switches keep tables of the
  MAC addresses of all the devices connected to the
  switch.
• Switches use these tables to determine which path
  to use when sending packets.
• However, unlike a bridge, a switch passes a
  packet only to its destination segment instead of
  to all segments other than the one it came from.

7
Bridges and Switches (Continued)

• Bridges and switches use MAC addresses to
  subdivide a network into physical segments.
• However, all the segments are still logically a
  single network because each host is communicating
  with other hosts on other segments using the MAC
  address rather than the IP address.
• As far as a host is concerned, it is not aware
  that a bridge or a switch exists in the network.

8
Subnetting

• A large network can be logically divided into two
  or more networks based on IP addresses rather
  than MAC addresses to reduce congestion.
• Each division is called a subnet and the process
  is called subnetting.

9
Subnet Masks

• How does the host know if a remote host is on the
  same network?
• An IP address is made up of the network ID and
  the host ID.
• The host is told what portion of the IP address
  identifies the network by an entry in the TCP/IP
  configuration settings.
• This entry is called the network mask, or subnet
  mask, and is used to define which portion of an
  IP address identifies the network and which
  portion identifies the host.

10
Subnet Masks (Continued)

• The network mask is a group of four 8-bit numbers
  separated by periods.

11
Subnet Masks (Continued)

• If the network IDs had been different, the host
  would not have attempted to resolve the IP
  address to the MAC address, but would have sent
  the data to the gateway to its network.
• A gateway is any device, typically a router, that
  provides access to another network.
• Subnet masks usually are not displayed as 32 bits
  separated by periods as they are in Table 6-1.

12
Selecting a Subnet Mask

• A network engineer carefully selects a subnet
  mask based on the number of subnets he needs and
  the number of hosts planned for each subnet.
• Table 6-3 on page 351 shows several examples of
  subnet masks and explains the number of hosts and
  subnets that can use each subnet mask.
• Subnetting is necessary when a large company is
  using a Class A, B, or C license for its entire
  network and wants to use that one license over
  several networks to prevent network congestion.

13
How Data Travels Across Interconnected Networks

• Figure 6-12 shows a simplified view of how
  networks work together to send data over the maze
  of many networks called the Internet.
• A router is a stateless device, meaning that it
  is unconcerned about the data that it is routing,
  but it is concerned about the destination address
  of that data.
• Networks are connected by routers, which belong
  to more than one network.

14
How Data Travels Across Interconnected Networks
(Continued)
15
Routers

• Routers are responsible for helping data travel
  across interconnected networks.
• A router can forward data to the correct network
  in a way that is similar to a switchs method.
• A router uses the most efficient path available
  to forward packets to their destination, which
  may be located across a great geographical
  distance.

16
Routers (Continued)

• A router can transmit a data packet to a remote
  network only if the higher-layer protocol that
  was used to produce the data packet can be routed
  to a remote network.
• A brouter, short for bridge and router, functions
  as both a bridge and a router.
• The device can forward routable protocols,
  including TCP/IP and IPX/SPX packets, and in
  these cases, is working as a router.

17
Routers (Continued)

• Packets that are not routable, such as NetBEUI
  packets, are forwarded to other local networks in
  the manner that a bridge would forward packets.
• Like switches, routers use tables to determine
  the best route by which to send the data to its
  destination.
• When routers communicate with other routers to
  build routing tables and determine availability
  of routes, one of several protocols is used RIP,
  OSPF, BGP, DVMRP, NLSP, or IGRP.

18
TCP/IP Routing

• Suppose a host computer wants to send data to
  another host.
• Remember that the host uses its subnet mask to
  decide if the destination host is on its own or
  another network.
• If the first host knows that the remote host is
  on its same network, it must discover the MAC
  address of the remote host.

19
TCP/IP Routing (Continued)

• If the sending host determines that the remote
  host is on a different network, it sends the data
  to the router, which is serving as the gateway to
  remote networks.
• When a packet arrives at a router, the router
  decides if the packet belongs to a host within
  its own local network or needs to be routed to a
  different network.

20
Routing Across Many Networks

• For routing across interconnected networks, each
  time a packet encounters a router, its TTL is
  reduced by one.
• If the router must send the packet over a network
  that cannot handle large packets, the router
  divides the packet into smaller packets.

21
Default Gateways

• Sometimes, a large network has more than one
  router, as shown in Figure 6-21on page 362, and
  so the network has more than one gateway to other
  networks.
• The network in the upper-left of the figure is
  250.1.2 and has two routers (D and E), each of
  which also belongs to other networks.

22
Default Gateways (Continued)

• Host E is designated as the default gateway,
  meaning that hosts on the 250.1.2 network send
  packets addressed to other networks to this
  gateway first.
• The other router Host D, is called the alternate
  gateway and is used if communication to the
  default gateway fails.

23
Domain Names on the Internet

• Domain names are assigned because IP address
  numbers are difficult to remember and because
  companies might want to change their IP addresses
  without also changing the Internet name by which
  the outside world knows them.
• The last segment, or suffix, of a domain name is
  called the top-level domain and tells you
  something about the function of the host.
• The first word in a domain name is used to
  identify a subcategory within the domain and is
  called a canonical name, or CNAME.

24
Assigning and Tracking Domain Names and IP
Addresses

• The organization responsible for overseeing this
  operation is the IANA (Internet Assigned Numbers
  Authority).
• Beginning in the spring of 1999, the
  responsibility for assigning and tracking domain
  names and IP addresses was transitioned from IANA
  to a nonprofit, private sector organization
  regulated by the U.S. Department of Commerce
  called ICANN (Internet Corporation for Assigned
  Names and Numbers).
• A company that can register these names and
  numbers must be approved by ICANN and is called a
  registrar.

25
Domain Name Resolution

• Domain names and IP addresses do not have to be
  permanently related.
• Two name resolution services track relationships
  between domain names and IP addresses DNS
  (Domain Name System, also called Domain Name
  Service) and Microsoft WINS (Windows Internet
  Naming Service).
• DNS is the more popular of the two because it
  works on all platforms.
• At the heart of DNS is a distributed database,
  which initially must be created manually.

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How DNS Works

• DNS has three logical components
• Computers searching for the IP address for a
  domain name, called resolvers
• Servers that contain the information relating
  domain names to IP addresses, called name servers
• The databases of information needed to resolve
  domain names and IP addresses, called namespaces

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How DNS Works (Continued)

• The process of discovering an IP address for a
  given domain name is called address resolution.
• It is also possible to find the domain name for a
  given IP address this process is called reverse
  resolution, or reverse mapping.
• Name servers are organized from the top down, as
  shown in Figure 6-24 on page 367.
• Network Solutions maintains servers called root
  servers that act as the highest level of
  authority when locating domain name information.

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How DNS Works (Continued)

• A network that supports DNS has two or more name
  servers, called the primary name server and
  secondary name server, which are shown in Figure
  6-24.
• The secondary server gets its information from
  the primary server, and is sometimes called the
  slave name server.
• An authoritative name server is the server that
  has the most current information about a domain
  name.

29
How DNS Works (Continued)

• The group of networks for which the name server
  is responsible collectively is called the name
  servers zone.
• A zone also can have a caching-only server that
  does not keep authoritative information, but only
  caches information as it is used in case it is
  needed again within a short period of time.

30
DNS Records

• Each name server holds a piece of the namespace,
  which is the database containing information
  needed to resolve domain names and IP addresses.
• A name server keeps the entries for each domain
  name that it knows about in a resource record, or
  DNS record.

31
Directory Server

• A directory server stores information about
  people, hosts, and other resources on the network
  in directories and provides this information to
  computers on the network.
• The information in a directory is read more often
  than it is written.

32
How Directories Work

• Directories follow an upside-down tree structure
  with the root at the top and branches underneath
  the root in a hierarchical structure.
• Directory servers sometimes use a protocol called
  LDAP (Lightweight Directory Access Protocol) to
  access directories, as illustrated in Figure
  6-28.
• LDAP was designed to run over TCP and can be used
  on the Internet or on an intranet.

33
How Directories Work (Continued)
34
How Directories Work (Continued)

• LDAP is a lighter version of DAP (Directory
  Access Protocol) LDAP has less code than DAP.
• Another important directory standard is X.500,
  which specifies how global directories can be
  structured.
• X.500 directories are designed to provide a
  listing of people within an organization so that
  anyone with Internet access can look someone up
  by country, organization, organizational level,
  or name.

35
Using Directories

• Directories and directory servers can serve
  various functions on networks and on the
  Internet.
• Directories on the Web are similar to search
  engines in the way they operate and provide
  information.

36
Cache Servers

• Microsoft Internet Explorer supports browser
  caching, which allows the user to indicate how
  much hard drive space should be allocated to Web
  caching.
• A cache server improves performance by caching
  data so that the number of requests to the
  Internet is reduced.

37
Cache Servers (Continued)

• Cache servers save Web pages and other files that
  users have requested so that when a page is
  requested again, it can be retrieved without
  accessing the Internet.
• Cache servers are placed between users and the
  Internet.
• A cache server can run on a system such as a
  proxy server or a router, or it can be set up as
  a dedicated computer system.

38
Mirrored Servers

• A mirrored server carries the same data and
  services as another server. These servers are
  exact replicas of the main servers that they
  mirror and are updated often to ensure that they
  contain the same data.
• Mirrored servers have two main purposes
• They reduce download time for users by handling
  some of the traffic for a frequently accessed Web
  site.
• They serve as backups for the main server in case
  it goes down.

39
Using a Mirrored Server to Handle Site Traffic

• Web sites that get a lot of traffic often need
  more than one server.
• If the traffic comes from different parts of the
  world, it might be necessary to have servers in
  different locations to provide the best service
  for international customers.

40
Using a Mirrored Server as a Backup Server

• A mirrored server acts as a very effective backup
  system.
• If the main server goes down, it is faster and
  easier to switch operation to a mirrored server
  than it is to restore information from disks and
  tapes.
• When a mirrored server is used as a backup for a
  server, it constantly copies short segments of
  files from the main server as they are updated.

41
Print Servers

• Print servers make printers available for shared
  use across a network or even across the Internet.
• Each print server can have several printers
  attached to it, and you can have more than one
  print server on a network, depending on the size
  of the network and the needs and locations of the
  users on it.

42
LPD Servers

• LPD (Line Printer Daemon) server is print server
  software that initially was developed on UNIX
  servers to handle print jobs, but is now
  supported by Windows Server 2003, Windows 2000
  Professional, and Windows NT Server.
• A client communicating with an LPD server can use
  two protocols, LPR and LPQ, which are part of the
  TCP/IP protocol suite.

43
LPD Servers (Continued)

• The client uses the LPR (Line Printer Remote)
  protocol to send print jobs over a TCP/IP network
  to the server.
• Clients that use LPR are sometimes referred to as
  LPR clients.
• A second protocol, LPQ (Line Printer Queue), is
  required for users to be able to check on the
  status of print jobs they have sent.

44
IPP

• Another useful and more recently developed
  printing protocol is IPP (Internet Printing
  Protocol).
• IPP, which also enables printing across LANs and
  the Internet, is generally more versatile than
  LPD and its associated services, and is more
  easily compatible with various operating systems.
• The greatest benefit of IPP is being able to find
  a printer by using the printers IP address or
  URL.
• With IPP, you can find any Internet-connected
  printer, print to it, and check the status of
  your print job.

45
Internet Security Appliances

• Internet security appliances, once called an
  Internet-in-a-box, are becoming a popular
  Internet access solution for small businesses.
• These devices combine a variety of technologies,
  such as Internet prevention, and other networking
  capabilities, into a single easy-to-manage unit.
• Remote Access Service (RAS) provides a way for a
  remote user to log on to the network using
  telephone lines and a modem.

46
Bandwidth Technologies

• Much attention is given to the amount of data
  that can travel over a given communication system
  in a given amount of time.
• This measure of data capacity is called
  bandwidth, also called data throughput or line
  speed.
• The greater the bandwidth, the faster the
  communication.
• A list of bandwidth technologies, their speeds,
  and their uses is shown in Table 6-6 on pages 381
  through 383.

47
Bandwidth Technologies Used to Connect to an ISP

• A local area network has much less need for data
  throughput than does a national backbone.
• Lying between these two extremes on the spectrum
  are many types of systems that require varying
  degrees of bandwidth.

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Regular Telephone Lines

• Regular telephone lines, the most common way to
  connect to an ISP, require an internal or
  external modem.
• When data packets travel over telephone lines,
  the Data Link layer protocol used is PPP or SLIP.
• PPP (Point-to-Point Protocol) most often is used
  to transmit TCP/IP packets from a computer
  connected to an ISP or intranet access point by
  telephone line.

49
Cable Modem

• Cable modem communication uses cable lines that
  already exist in millions of households in the
  United States.
• Just as with cable TV, cable modems are always
  connected.
• A cable modem is an example of broadband media.
• Broadband refers to any type of networking media
  that carries more than one type of transmission.

50
PPPoE (Point-to-Point Protocol over Ethernet)

• PPoE (Point-to-Point Protocol over Ethernet) is a
  protocol that adapts PPP to work with Ethernet.
• PPPoE describes how the computer is to interact
  with the converter box or modem when the two are
  connected by an Ethernet cable connected to an
  Ethernet network card in the computer.
• PPPoE gives the user the security and
  authentication that is offered with PPP.
• PPPoE also sets standards for networks to connect
  to the Internet via DSL modems and other
  high-speed access services.

51
ISDN

• ISDN (Integrated Services Digital Network) is a
  technology developed in the 1980s that uses
  regular telephone lines, and is accessed by a
  dial-up connection.
• ISDN is actually an early implementation of DSL.

52
DSL

• In the race to produce a fast data transmission
  technology that is affordable for home use and
  that offers a direct connection rather than a
  dial-up connection, the telephone industry has
  developed several similar technologies that
  collectively are called DSL (Digital Subscriber
  Line).
• Table 6-7 on page 390 lists common variations of
  DSL.
• The most popular version of DSL is ADSL
  (Asymmetric Digital Subscriber Line), which is 50
  times faster than ISDN and is direct connect.

53
Satellite Connections to the Internet

• People who live in remote areas and want
  high-speed Internet connections often are limited
  in their choices.
• DSL and cable modems might not work where they
  live, but satellite access is available from
  almost anywhere.
• Technology is even being developed to use
  satellites to offer Internet access on commercial
  airlines.
• New technology allows data to be transmitted both
  ways over the satellite so that telephone line
  connections are not needed.

54
Wireless Connections

• Wireless is an important technology for mobile
  devices and for Internet access in remote
  locations where other methods are not an option.
• For Internet access, two popular applications of
  wireless are fixed-point wireless, sometimes
  called Wireless Local Loop (WLL), and mobile
  wireless.
• With fixed-point wireless, an antenna sits on
  your house or office building and communicates
  with a base station antenna.

55
Using Wireless Technology to Browse the Internet

• Most of the wireless devices that advertise
  Internet access are menu-driven, which means that
  you select where you want to go from a menu
  instead of typing in a URL.
• After the browser has been launched, you might be
  charged for the time you are connected.
• Most Web sites still are not designed with
  wireless technology in mind, and some devices run
  software that converts HTML so it can be
  displayed on wireless devices.
• This conversion process is called clipping
  because it takes out, or clips, the images and
  leaves a site with all text that uses menus to
  navigate.

56
Wireless Application Protocol

• The high demand for wireless access to the
  Internet, including Web pages and e-mail, led to
  the creation of the WAP (Wireless Application
  Protocol).
• One goal of WAP is to bridge the gap between the
  needs of traditional Internet access devices and
  wireless Internet access devices.
• WAP is a communication standard designed for
  mobile Internet access.
• One feature of WAP is WML (Wireless Markup
  Language).

57
Wireless Application Protocol (Continued)

• WML is a markup language that is very similar to
  HTML, but it is derived from XML (Extensible
  Markup Language).
• WML files are called decks and are divided into
  cards.
• Cards are sections of the deck that fit onto one
  screen.

58
Uses of Wireless Devices

• One popular service that is being provided to
  customers with wireless Internet devices is
  instant notification, or alerts.
• If you were invested heavily in a particular
  stock, for example, wouldnt it be nice to be
  notified immediately if the value changed?

59
T Lines and E Lines

• The first successful system that supported
  digitized voiced transmission was introduced in
  the 1960s and was called a T-carrier.
• A T-carrier works with a leased digital
  communications line provided through a common
  carrier, such as Bellsouth or ATT.
• The leased lines are permanent connections that
  use multiplexing, a process of dividing a single
  channel into multiple channels that can be used
  to carry voice, data, video, or other signals.

60
T Lines and E Lines (Continued)

• The E-carrier is the European equivalent of the
  American T-carrier.
• The E-carrier is a digital transmission format
  devised by ITU at www.itu.int.
• A fractional T1 line is an option for
  organizations that dont need a full T1 line.
• The fractional T1 allows businesses to lease some
  of the channels of a T1 line rather than leasing
  all 24 channels.

61
X.25 and Frame Relay

• Both X.25 and frame relay are packet-switching
  communication protocols designed for
  long-distance data transmission rather than the
  circuit-switching technology used by the
  telephone system.
• Both X.25 and frame relay use a PVC (permanent
  virtual circuit).
• PVC is a permanent, logical connection between
  two nodes.
• PVCs are not dedicated lines, like the
  T-carriers.
• The biggest advantage of X.25 and frame relay is
  that you only have to pay for the amount of
  bandwidth you require.

62
ATM

• ATM (Asynchronous Transfer Mode) is a very fast
  network technology that can be used with LANs, as
  well as WANs.
• It uses fixed-length packets, called cells, to
  transmit data, voice, video, and frame relay
  traffic.
• ATMs also use virtual circuits, meaning that the
  two endpoints are stationary, but the paths
  between these two endpoints can change.
• They can use either PVCs or SVCs.
• SVCs (switched virtual circuits) are logical,
  point-to-point connections that depend on the ATM
  to decide the best path to send the data.

63
Mesh Topology

• A mesh topology provides multiple point-to-point
  links between routers in a wide area network,
  giving more than one choice on how data can
  travel from router to router.
• In a mesh topology, a router searches out
  multiple paths and determines the best path to
  take.

64
Summary

• To relieve congestion, a network can be segmented
  into smaller networks by using a bridge, switch,
  or router.
• A large network logically can be divided into
  subnets by using a subnet mask, which takes a few
  bits from the network portion of the IP addresses
  on a network to define the subnets on the network.

65
Summary (Continued)

• Domain names are an easy way to remember an IP
  address, but also can be assigned to different
  folders on a host so that a host can have many
  domain names assigned to it.
• Web caching can be used to store frequently used
  Web pages in a temporary place to decrease
  download time.
• Packet-switching divides data into packets and
  sends each packet independently.