Chapter 13 Internetworking Technologies

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Chapter 13Internetworking Technologies

• Part III Wide Area Networks and Internetworking
  Technologies

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Topics Addressed in Chapter 13

• Internetworking technologies and the OSI model
• Business rationale for internetworking
  technologies
• Using repeaters to connect LAN segments
• Using bridges to connect two LANs
• Routers and network layer connections
• Using gateways to connect networks above the
  network layer
• Internetworking via switches
• Remote access technologies
• Wireless access to corporate networks
• Intranets and extranets Web-based internetworking

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Internetworking and the OSI Model

• Internetworking technologies are used to
  interconnect networks
• The OSI reference model provides an appropriate
  context for understanding internetworking
  technologies (see Figure 13-3)
• Although some internetworking technologies span
  two or more layers of the OSI model, most can be
  classified as physical layer, data link layer,
  network layer, or higher layer technologies

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Figure 13-3
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Physical Layer Technologies

• One of the main responsibilities of physical
  layer interconnection technologies is to overcome
  signal attenuation (see Figure 13-1)
• Repeaters are used in digital communication
  systems
• Amplifiers do this in analog systems
• Repeaters are also used to overcome distance
  limitations in this role they function as signal
  relay stations (see Figure 13-2)
• Repeaters can be standalone devices and be used
  for media conversion.
• Repeating capabilities are typically included in
  LAN shared media hubs, patch panels, and
  punchdown blocks
• Optical repeaters are available for fiber optic
  networks

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Figure 13-1
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Data Link Layer Connections

• Three key functions of data link layer protocols
  are data delineation, error detection, and
  address formatting
• Bridges are used to interconnect two LANs at the
  data link layer (see Figure 13-4)
• Bridges have more intelligence than physical
  layer technologies they have to examine (filter)
  data link layer frames transmitted in one network
  to determine if they should be forwarded to the
  other network (see Figure 13-5)
• Layer 2 switches are also used to connect two
  networks at the data link layer

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Figure 13-5
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Network Layer Connections

• The network layer of the OSI reference model is
  responsible for packet routing in networks with
  multiple alternative paths from sender to
  receiver (see Figure 13-6)
• Routers are widely used network layer
  internetworking technologies
• After determining the destination address of the
  recipient, a router chooses the best route for a
  packet based on routing tables and routing
  algorithms
• Layer 3 switches have routing capabilities

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Figure 13-6
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Higher Layer Connections

• Network connections that operate above the
  network layer are generically called gateways
• Gateways often support protocol conversion
  because the networks they interconnect use
  different network layer protocols (see Figure
  13-7)

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Figure 13-7
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Business Rationale for Internetworking
Technologies

• Internetworking technologies enable LANs to be
  interconnected. LANs can also be connected to
  LANs. In addition, WANs can be interconnected.
  Hence, internetworking technologies are used by
  businesses to create enterprise-wide networks
• Internetworking technologies can also be used to
  form interorganizational systems that connect an
  organization and one or more business partners
• The ability to forge larger networks from smaller
  ones facilitates resource sharing and
  communication enterprise-wide

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Repeaters Connecting LAN Segments

• Repeaters are used in LANs to overcome signal
  attenuation and distance limitations
• They are also used to connect LAN segments (see
  Figures 13-8 and 13-9)
• Some LAN standards specify the maximum number of
  LAN segments that can be created
• Repeater capabilities are specified in Table
  13-1.
• Repeater limitations include insensitivity to
  data errors and the recreation of collisions that
  originate in one segment to all other segments

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Figure 13-8
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Figure 13-9
Table 13-1
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Bridges Connecting Two LANs

• Bridges are used to connect two LANs at the data
  link layer of the OSI model (see Figure 13-11)
• Bridges possess more intelligence than repeaters
  and are typically more costly
• Unlike repeaters, bridges handle complete frames
• This means that they can isolate problems to a
  LAN and reduce the likelihood of transferring
  noise or collisions from one network to the other
• Bridges listen to traffic on each network they
  are often called promiscuous listening
  technologies
• Bridges are typically implemented as standalone
  devices

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Figure 13-11
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Bridge Functionality

• When a bridge receives a data link layer frame
  from one network (or segment), it verifies that
  it is correctly formatted and if necessary,
  forwards it to the other network.Two LANs
  connected by a bridge behave like a single LAN
• Frame filtering is one of the most important
  functions performed by a bridge this is the
  process of reading the destination address in the
  frames header and determining if it should be
  forwarded to the other networkFiltering rates
  are measured in frames or packets per second
• Forwarding is the process used by a bridge to
  send a frame from one network to the other
• Format conversion is necessary if the bridge
  connects LANs with dissimilar data link protocols
• Bridges that connect dissimilar LANs are called
  translating bridges (see Figure 13-12)
• Forwarding rates are measured in frames per
  second
• Additional bridge functions are summarized in
  Table 13-2

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Figure 13-12
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Table 13-2
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Types of Bridges

• Various kinds of bridges exist including
• Transparent connect two similar LANs
• Translating connect two different LANs
• Learning (adaptive) builds routing tables from
  network traffic
• The spanning tree algorithm enables bridges to
  exchange routing information with each other
• Source routing bridges used in token ring
  networks
• Remote bridges used to interconnect LANs via WAN
  services (see Figure 13-14 and Table 13-4)
• Wireless can be used to bridge remote LANs
  located within a few miles of each other

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Figure 13-14
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Routers Network Layer Connections

• Key network layer functions include
• Routing forwarding data to its destination along
  its best route
• Network control exchanging node status
  information among routing nodes to facilitate the
  best routing for messages
• Congestion control attempting to reduce
  transmission delays by sharing information about
  network traffic and message queue length among
  routers or network switches

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Message Routing Processes

• Message routing processes can be centralized or
  distributed
• In networks that centrally determine packet
  routing, one router is designated as the network
  routing manager to which all other routers
  periodically forward network status information
• Distributed routing determination requires each
  router to periodically send network status
  updates to the other routers in the network
• Routing can be categorized as static, weighted or
  dynamic
• In static routing, the same path between two
  nodes is always used
• In weighted routing, each alternative path is
  given a weight based on perceived use random
  numbers are generated for incoming packets to the
  same destination to determine which path to use
  (see Figure 13-16)
• Dynamic (adaptive) routing attempts to select the
  best current route based on network conditions
  it considers path failures and congestion (see
  Figure 13-17)

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Figure 13-16
Figure 13-17
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IP Routing

• When an Internet node sends a message to another
  Internet node, it must know the destination
  nodes IP address
• This may be resolved from a URL using the
  Internets domain name system
• The IP routing process is summarized in Figure
  13-20
• IP routing may also be used in networks that are
  not attached to the Internet (see Figure 13-21)

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Figure 13-20
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Types of Routers

• Three types of routers can be identified for
  organizations whose networks are attached to the
  Internet
• Internal used to route packets between the
  subnets or the networks included in a particular
  subnet
• Border used to route messages between an
  organizations network and the Internet
• External route messages between border routers
  across the Internet backbone (these are also
  called Internet backbone routers)
• These are illustrated in Figure 13-19
• Dial-up routers enable geographically dispersed
  LANs to be connected over dial-up digital WAN
  services such as ISDN (see Figure 13-22)
• High-speed routers, such as edge routers, enable
  network traffic to be routed over high-speed ATM
  networks or SONET services
• Terabit routers are capable of forwarding
  hundreds of millions of packets per second and
  have throughput rates of more than one trillion
  bits per second

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Figure 13-19
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Figure 13-22
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Router Functionality

• Like bridges, filtering and forwarding rates are
  often used as router performance measures
• Unlike bridges, routers only process packets that
  are addressed to them
• Also unlike bridges, forwarding decisions are
  based on destination addresses in network layer
  packet headers
• Routers can also be used to limit access to a
  network many have firewall capabilities
• Multiprotocol routers are capable of forwarding
  messages using more than one network layer
  protocols
• Encapsulation may be used to enable non-routable
  data link protocols, such as SDLC, to be routed
  over TCP/IP networks

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Routing Protocols

• Routing protocols enable routers to adapt to
  changes in network conditions and topologies
  they enable routers to exchange network status
  updates in order to keep the information in
  routing tables current
• There are three major categories of routing
  protocols
• Distance vector protocols base routing decisions
  on the distance (number of hops) to every other
  router in the network
• Examples include RIP (Routing Information
  Protocol) and EIGRP (Enhanced Interior Gateway
  Routing Protocol)
• Link state protocols compute best routes by
  consulting a complete copy of the network
  topology and traffic conditions
• Examples include OSPF (Open Shortest Path First),
  NLSP (NetWare Link Services Protocol) , and IS-IS
  (Intermediate System-to-Intermediate System)
• Path vector protocols maintain comprehensive
  lists of known routes and networks between
  senders and receivers.
• BGP (Border Gateway Protocol) is an example

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Gateways Connecting Networks Above the Network
Layer

• Gateways connect dissimilar networks networks
  that do not share a common physical, data link,
  or network layer protocol
• A gateway can connect two or more networks above
  the network layer of the OSI model
• A gateway reconciles differences between the
  networks it connects and serves as a protocol
  converter
• In some instances, a complete network or WAN
  service may serve as a gateway between two
  networks (see Figure 13-23) this is possible if
  gateways exist to connect each of the two
  networks to the WAN service

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Figure 13-23
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Switches

• Switches are widely used to interconnect
  networks. Like other internetworking
  technologies, these correspond to OSI model
  layers (see Figure 13-24)
• These include
• Layer 2 switches function like bridges by
  sending frames to destinations based on MAC
  addresses (see Figure 13-25)
• Layer 3 switches are capable of layer 2
  switching and layer three routing both layer 2
  and layer 3 switches may be used to create
  virtual LANs (VLANs)
• Layer 4 switches can route TCP/IP messages based
  on well known port addresses in TCP headers in
  addition to layer 2 or layer 3 addresses
• Backbone attached LAN switches enable switched
  connections between devices attached to the same
  LAN as well as switched access to a high-speed
  backbone network or router (see Figure 13-26)
• Backbone switches enable switched
  interconnections among various types of LANs as
  well as switched access between LANs and a
  backbone network or WAN services (see Figure
  13-27)

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Figure 13-24
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Figure 13-25
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Figure 13-26
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Figure 13-27
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Remote Access Technologies

• Remote access technologies provide network access
  to teleworkers
• Two major types of remote access exist
• Remote client (node) computing occurs when client
  applications on remote nodes communicate with
  server applications via dial-up or other WAN
  links (see Figure 13-28a)
• Remote control applications are run on the server
  rather than the client remote nodes function as
  terminals or thin clients (see Figure 13-28b)
• Three major approaches exist for remote users to
  access LAN resources (see Figure 13-29)
• Dial-in connection to a LAN-attached
  microcomputer
• Dial-in connection to a LAN modem
• A LAN modem is essentially a modem with a NIC
• Dial-in connection to a communication server (see
  Figure 13-30)
• A communication server provides dial-in and
  dial-out services for LAN users these are also
  called remote access servers, remote node
  servers, and telecommuting servers

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Figure 13-29
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Figure 13-30
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Wireless Access to Corporate Networks

• Explosive growth in wireless communication
  technologies is fueling interest in wireless
  internetworking technologies
• Two important wireless internetworking
  technologies are wireless bridges and mobile IP
• Wireless bridges enable organizations to link
  LANs that are located within a few miles of each
  other
• These enable organizations to avoid carrier
  service charges
• Mobile IP enables users to roam among wireless
  LANs
• Mobile IP clients must be installed on each
  mobile wireless device to enable it to
  communicate with mobile IP servers or routers in
  corporate network offices

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Interconnections via Web Technologies

• Organizations are increasingly leveraging TCP/IP
  applications to create intranets and extranets
• Firewalls enable remote users to access corporate
  intranets from virtually anywhere via Web
  browsers
• Clientless network operating systems, such as
  NetWare 6, also enable remote users to access
  corporate network resources via Web browsers

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Chapter 13Internetworking Technologies

• Part III Wide Area Networks and Internetworking
  Technologies