Linux+ Guide to Linux Certification

							HANDS-ON NETWORKING
FUNDAMENTALS




Chapter 5
Devices for Connecting Networks
LAN TRANSMISSION DEVICES
•   Uses of LAN transmission equipment
    –   Connecting devices on a single network
    –   Creating and linking multiple networks or
        subnetworks
    –   Setting up some enterprise networks
•   Connecting devices that will be discussed
    –   repeaters,
    –   MAUs,
    –   hubs,
    –   bridges,
    –   routers
    –   switches,
    –   gateways

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REPEATER
•   OSI Physical Layer device
•   Connects two or more cable segments
•   Retransmits incoming signal to all other segments
•   Cable segment is run within IEEE specifications
•   Performs four Physical layer functions
    –   Filter out signal disturbance caused by EMI and RFI
    –   Amplify and reshape incoming signal
    –   Retime the signal (in Ethernet applications)
    –   Reproduce the signal on all cable runs



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REPEATER (CONTINUED)
•   Uses of repeaters
    –   Extend cable segments
    –   Increase number of nodes beyond segment
    –   Sense network problem and shut down segment
    –   Connect to components in other network devices
    –   Amplify and retime signals
    –   Connect segments using different media
    –   Increase communication distance of T-carrier lines
•   Collision domain: segments where collisions
    occur
    –   Caused by two or more nodes transmitting at once

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REPEATER (CONTINUED)

   Two kinds of repeaters
     Class I: only one can be used between two end
      nodes
     Class II: one or two between two end nodes




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HUB
 Central network device connecting nodes in
  star
 Functions of a hub
     Centrally   connect multiple nodes into one
      network
     Consolidate the network backbone
     Provide connections for several different media
      types



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HUB (CONTINUED)
•   Workgroup hubs: form participants into
    workgroup
    –   May be connected to another device (switch,
        router)
    –   Are stackable (stacked on top of each other)
•   Intelligent (managed) hub
    –   Gathers information about network performance
    –   Enables remote shut down of port or entire hub
•   Hubs can partition network segments (like
    repeaters)

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BRIDGE

•   Network device connecting LAN segments
•   Functions of a bridge
    –   Extend LAN when maximum connection limit
        reached
         •   Example: the 30-node limit on an Ethernet bus
    –   Extend a LAN beyond the length limit
         •   Example: beyond 185 meters for a Thinnet segment
    –   Segment LANs to reduce data traffic bottlenecks
    –   Prevent unauthorized access to a LAN
    –   Examine frame's physical destination address
    –   Occurs at MAC sub layer of OSI Data Link layer

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BRIDGE (CONTINUED)

•   Three frame scenarios
    –   Destination on same segment as source
         •   Bridge drops frame, since no forwarding needed
    –   Destination on another segment known to bridge
         •   Bridge transmits frame to the known segment only
    –   Destination segment not known to bridge
         •   Bridge transmits frame to all segments but source
•   Protocol independent
    –   Look only at MAC address
    –   May forward different protocols on same network

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BRIDGE (CONTINUED)
•   Translational bridge
    –   Converts frame to new access method and media type
    –   Example: from Token Ring to Ethernet
         •   Discards addressing information not used in Ethernet
•   Three primary bridge functions
    –   Learning: learn network topology and device
        addresses
         •   Information stored in a bridging table
    –   Filtering: do not flood certain frames, discard others
         •   Enables bridge to used for security purposes
    –   Forwarding: transmit frames to destination
         •   Based on data built-in to bridging table

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BRIDGE (CONTINUED)

•   Multiport bridges tie several LANs into one
    network
•   Advantages of bridge over repeaters and hubs
    –   Ability to segment network traffic
    –   May serve as a firewall to keep intruders out
•   Two types of bridges
    –   Local: directly connects two LANs in close proximity
         •   Also used to segment traffic to reduce bottlenecks
    –   Remote: join distant networks
         •   Used to join networks in different cities or states
•   Wireless bridges: a subclass of local bridges
    –   Link to nodes equipped with wireless NIC (WNIC)

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SWITCH

•   Dual purpose
    –   To provide bridging capacity
    –   To increase bandwidth
•   Bridge-like characteristics of switch
    –   Operates at Data Link MAC sub layer
    –   Uses table information to filter and forward traffic




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SWITCH (CONTINUED)

•   Reduces collisions and improves bandwidth
    on Ethernet
    –   Example: hub with eight 100 Mbps segments
         •   Has capacity of 8 x 100 (800) Mbps
•   Managed switches have intelligence options
    –   Options similar to those of managed hub




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MULTISTATION ACCESS UNIT
•   Multistation access unit (MAU or MSAU)
    –   Central hub on a token ring network
    –   May have intelligence built-in to detect problems
         •   Smart multistation access unit (SMAU)
•   Tasks performed by MAU
    –   Connect nodes in a logical ring upon a physical star
    –   Move the token and frames around the ring
    –   Amplify data signals
    –   Expand token ring network by daisy-chain
        connections
    –   Provide for orderly movement of data
    –   Shut down ports to malfunctioning nodes
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MULTISTATION ACCESS UNIT (CONTINUED)

 Functions at OSI Physical and Data Link
  layers
 Can interconnect in daisy-chain fashion
     Ring in (RI), ring out (RO) ports linked with patch
      cable
   Control Access Unit (CAU): stacks multiple
    MAUs into one logical unit



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TOKEN RING SOURCE-ROUTE BRIDGE

•   Source-route bridges used in token rings
    –   Perform routing at the OSI Network layer
    –   Store and forward packets indicated by specified
        route
•   Process of sending a packet
    –   Explorer packet travels to destination, returns to
        source
    –   Path taken by real packet determined by three factors
         •   Route taken by explorer packet received back
         •   Minimum number of hops to destination
         •   Path that can enable the largest packet size
•   Hop: packet transfer between networks
    –   Route selected based on fewest hops (shortest path)
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GATEWAY
•   Software or hardware interface
    –   Enables two networked or software systems to link
•   Functions of a gateway
    –   Convert common protocols to specialized type
    –   Convert message formats from one format to
        another
    –   Translate different addressing schemes
    –   Link a host computer to a LAN
    –   Provide terminal emulation for connections to host
    –   Direct electronic mail to the right network
        destination
    –   Connect networks with different architectures
•   Can function at any OSI layer
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Table 5 – 2: See Textbook for Details   23
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