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Network Devices

Network Devices. Repeaters, hubs, bridges, switches, routers, NIC’s. Devices and the layers at which they operate. NIC’s ( Network Interface Cards ). This NIC has interfaces for twisted pair, thicknet, and thinnet connectors. Repeaters.

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Network Devices

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  1. Network Devices Repeaters, hubs, bridges, switches, routers, NIC’s

  2. Devices and the layers at which they operate

  3. NIC’s (Network Interface Cards) • This NIC has interfaces for twisted pair, thicknet, and thinnet connectors.

  4. Repeaters • Signal attenuation or signal loss – signal degrades over distance • Repeaters clean, amplify, and resend signals that are weakened by long cable length. • Built-in to hubs or switches

  5. Hubs • OSI layer 1 hardware • Hubs regenerate and retime network signals • Hubs propagate signals through the network • They cannot filter network traffic • They cannot determine best path • They are used as network concentration points • They are really multi-port repeaters • Uplink port – crossover mode or straight through mode

  6. Bridges • A layer 2 device designed to create two or more LAN segments, each of which is a separate collision domain. • The purpose is to filter traffic on a LAN, to keep local traffic local, yet allow connectivity to other segments of the network. • Filter traffic by looking at the MAC address • Frame filtering

  7. Bridges • If the frame is addressed to a MAC address on the local side of the bridge, it is not forwarded to the other segment • MAC addresses on the other segment are forwarded • Bridges maintain a MAC address table for both segments they are connected to

  8. Cycle of bridges • Bridged network can span many segments • Broadcasts are sent to all segments

  9. BridgesDistributed Spanning Tree • If all bridges forward broadcasts, infinite loops can occur • Bridges perform DST on boot to determine which bridges will not forward broadcasts

  10. Switched networks • Shared ethernet networks perform best when kept to 30-40 percent full capacity • This is a result of CSMA/CD • A LAN switch is a high-speed multiport bridge which segments each port into its own collision domain and can access the full bandwidth

  11. Devices and the layers at which they operate

  12. Switches • Each port is a simulated segment to itself

  13. Store and Forward Switches • Do error checking on each frame after the entire frame has arrived into the switch • If the error checking algorithm determines there is no error, the switch looks in its MAC address table for the port to which to forward the destination device • Highly reliable because doesn’t forward bad frames • Slower than other types of switches because it holds on to each frame until it is completely received to check for errors before forwarding

  14. Cut Through Switch • Faster than store and forward because doesn’t perform error checking on frames • Reads address information for each frame as the frames enter the switch • After looking up the port of the destination device, frame is forwarded • Forwards bad frames • Performance penalty because bad frames can’t be used and replacement frames must be sent which creates additional traffic

  15. Fragment free cut through switch • Combines speed of cut through switch with error checking functionality • Forwards all frames initially, but determines that if a particular port is receiving too many bad frames, it reconfigures the port to store and forward mode • Preferred switching solution

  16. Unmanaged/Intelligent switches • Unmanaged – provides LAN’s with all the benefits of switching • Fine in small networks • Intelligent switches tracks and reports LAN performance statistics • Have a database ASIC (application specific integrated circuit) on board to collect and store data which you view through a software interface

  17. Layer 3 switch • By definition a switch filters or forwards frames based on MAC addresses. This makes a switch a layer 2 device. • Now we have layer 3 switches which have routing capability. If a data frame can’t be switched it is routed. • Each port is a separate LAN port, but the forwarding engine actually calculates and stores routes based on IP addresses, not MAC addresses • Usually support only IP or IP and IPX

  18. VLAN Switches • Virtual local area network • Each port on a switch defines a collision domain • The entire switch forms a single broadcast domain • VLANs can define multiple broadcast domains • Network traffic that is directed to all computers on the network can be segmented to transmit only on a specific VLAN. • Improves bandwidth on a the VLAN’s because each VLAN filters the network-to-network broadcast traffic as well as the collision traffic from other VLAN’s

  19. Physical Layer Broadcast • Physical layer broadcasts – implemented by non-switched Ethernet networks through shared cabling and hubs • Each bit that is transmitted is physically received by every station • Switches and VLAN’s don’t do physical layer broadcasts

  20. MAC-level broadcast • MAC-level broadcast – deal with how to handle MAC level broadcast frames; that is the data frames that have a broadcast destination MAC address • MAC-level broadcast frames are addressed to all MAC addresses on a given network (not a network segment, but an actual network as defined by its network address) • A regular switch forwards all broadcast frames out all ports, but a VLAN switch forwards broadcast frames only to ports that are part of the same VLAN • Multiple switches can be part of the same VLAN

  21. VLAN Switches • None of the VLAN’s can communicate unless each VLAN is connected to a router or layer 3 switch • Each VLAN is separating collision traffic associated with MAC Addresses (layer 2) and each VLAN is separating the network-to-network broadcast traffic. In other words each VLAN is acting as a separate network so a layer 3 device is necessary for them to communicate

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