Network Devices

Summary

  • Network administrators use devices to control and extend the usable size of a network
  • These devices include repeaters, hubs, bridges, switches, routers, brouters, and gateways
  • Repeaters work against attenuation by cleaning and repeating signals that they receive on a network
  • Repeaters work at the Physical layer of the OSI model
  • They cannot connect different network architectures
  • Repeaters do not reduce network traffic or segment the network
  • A hub ties several networking cables together to create a link between different stations on a network
  • An active hub has its own electrical power and acts as a repeater, whereas a passive hub provides no signal regeneration
  • Hubs operate at the Physical layer of the OSI model and do not segment the network
  • Network segmentation is the process of isolating hosts onto smaller segments to reduce the possibility of collisions
  • Bridges and switches are two devices commonly used to segment networks
  • Bridges provide network segmentation by examining the MAC address that is sent in the data frame
  • Bridges can use transparent bridging or source-route bridging to determine which segment includes a specific physical address
  • Bridges operate at the Data Link layer of the OSI model
  • Switches increase network performance by reducing the number of frames transmitted to the rest of a network
  • They do this by opening a virtual circuit between the source and the destination
  • Switches operate at the Data Link layer of the OSI model
  • Routers operate at the Network layer of the OSI model and provide filtering and network-traffic control on LANs and WANs
  • They can connect multiple segments and networks
  • On a TCP/IP network, routers use IP addresses to route packets to the correct network segment
  • Routers use information from routing tables to move packets from one network to another
  • A brouter is a hybrid device that functions both as a bridge for non-routable protocols and as a router for routable protocols
  • Brouters operate at both the Data Link and Network layers
  • Gateways are usually a combination of hardware and software and are used to translate between different protocols
  • They usually operate at layer 4 and above in the OSI model

Repeaters

  • Length of cable used influence the quality of communication
  • Attenuation
  • Repeaters repeat signals
  • Repeaters only work with the physical signal
  • Cannot reformat, resize, or manipulate the data
  • Physical layer (layer 1) device

Hubs

  • Generic connection device

–Physical layer

  • Connect several networking cables together
  • Active hubs

–Multiport repeaters

  • Passive hubs
  • Hubs and topology
  • Advantages of using repeaters–Extend network physical distance

    –Do not seriously affect network performance

    –Special repeaters connect different media

    • Copper to fiber

    Disadvantages of using repeaters

    –Cannot connect different network architectures

    • Token Ring and Ethernet

    Cannot reduce network traffic

    • Do not segment the network

    –Repeat everything without discrimination

    –Number of repeaters must be limited

    • Repeaters are part of a collision domain

Wireless Access Points

  • Wireless local area networks (WLANs)
  • Wireless access points provide cell-based areas

–Contains radio transceiver

–Function like a hub

–Bandwidth is shared

–May also function as a wireless repeater

  • Wireless clients

Network Segmentation

  • Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
  • Problems occur with too many nodes on the same network segment or collision domain
  • Collision

–Back off algorithm

–Back off period

  • Segmentation

–Collisions and retransmissions are reduced

Contention for bandwidth is reduced

Bridges

  • Operate at the Data Link layer
  • Forward or drop frames
  • Cannot filter broadcasts
  • MAC to segment # table
  • MAC to segment # table initial development

Transparent Bridges

  • Also called learning bridges
  • Build a table of MAC addresses as frames arrive
  • Ethernet networks use transparent bridges
  • Token Ring networks use source-routing bridges

Source-Routing Bridges

  • Used in Token Ring networks
  • Rely of source of the frame transmission
  • Explorer frames

Translation Bridges

  • Connect networks with different network architecture
  • Example:

–Token ring connecting to Ethernet

Advantages Of  Using Bridges

–Extend physical network

–Reduce network traffic with minor segmentation

–Creates separate collision domains

–Reduce collisions

–Connect different architecture

Disadvantages of using bridges

–Slower that repeaters due to filtering

–Do not filter broadcasts

–More expensive than repeaters

 

Switches

  • Operate at the Data Link layer
  • Increase network performance
  • Virtual circuits between source and destination
  • Micro segmentation
  • Multiple virtual circuits are called “switched bandwidth”
  • Between two computers using a switch two collision domains are created each with dedicated bandwidth
  • Between two hubs using a switch two collision domains are created each with shared bandwidth
  • Filter based on MAC addresses
  • Build tables in memory

Advantages Of  Using Switches

–Increase available network bandwidth

–Reduced workload, computers only receive packets intended for them specifically

–Increase network performance

–Smaller collision domains

Disadvantages of using Switches

–More expensive than hubs and bridges

–Difficult to trace network connectivity problems through a switch

–Does not filter broadcast traffic

Routers

  • Provide filtering and network traffic control
  • Used on LANs and WANs
  • Connect multiple segments and networks
  • Multiple routers create an “internetwork”
  • Operate at the Network layer
  • Create a table to determine how to forward packets
  • Filtering and traffic control base on logical addresses

Physical Versus Logical Addresses

  • MAC addresses

–Data Link layer application

–Used by switches, bridges, and routers

–Used for directly connected devices

  • Logical addresses

–Network and transport protocols dictate the format of the logical network layer address

–TCP/IP, IPX/SPX

–IP addresses are assigned manually or by software

Advantages Of  Using Routers

–Can connect networks of different architecture

  • Token Ring to Ethernet

–Choose best path through or to a network

–Create smaller collision domains

–Create smaller broadcast domains

Disadvantages of using Routers

–Only work with routable protocols

–More expensive than hubs, bridges, and switches

–Routing table updates consume bandwidth

–Increase latency due to a greater degree of packet filtering and/or analyzing

Connected Router in the network

Brouters

  • Hybrid device
  • Functions as a router for routable protocols
  • Functions as a bridge for non-routable protocols
  • Operates at Data Link and Network layers

Gateways

    • A gateway is a combination of hardware and software
    • Translate between different protocol suites
    • Operates on all 7 layers of the OSI model
    • Most negative on network performance

    –Latency

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