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Objectives

Learn about the different types of bridging - transparent, source route, and translate, and understand how transparent bridges operate. Explore the advantages and disadvantages of bridging and gain knowledge of LAN switches fundamentals.

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Objectives

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  1. Objectives After completing this chapter you will be able to: • Describe the different types of bridging: Transparent, Source Route and Translate • Describe how Transparent Bridges operate • Outline the advantages and disadvantages of bridging • Describe the fundamentals of LAN switches

  2. SYSTEM B SYSTEM A Data Data A A P Data P Data Data Data S S T Data T Data Router Data Data N N Bridge Data Data D D Repeater 101100011110101010010 101100011110101010010 OSI Model

  3. Network Segment A Network Segment A Network Segment A REPEATER BRIDGE or SWITCH ROUTER Network Segment A Network Segment B Network Segment B C.D. B.D. C.D. B.D. C.D. B.D. Single Broadcast Domain Single Collision Domain Single Broadcast Domain Two Separate Collision Domains Two Separate Broadcast Domains Two Separate Collision Domains Repeaters v Routers / Bridges v Routers

  4. Different Types of Bridging • Source Route Bridges Developed by IBM for use in Token Ring Networks. The entire route to a destination is predetermined prior to sending data. • Transparent Bridges Developed by Digital Equipment Corporation (DEC) for use in Ethernet networks. Frames are forwarded one hop at a time towards the destination

  5. 4 LAN B 5 Discovery LAN A Response 1 6 LAN C 2 7 8 3 Source Route Bridging

  6. Source Address table Address Interface 1 A 2 A 3 A 4 B 5 B 6 B 7 C 8 C 9 C Transparent Bridging 5 4 B 6 1 A C BRIDGE 8 2 7 3 9

  7. 5 6 4 B 1 A BRIDGE C 2 8 3 Source 1 - Destination 4 7 9 Source 4 - Destination 1 Transparent Bridge Operation - Example

  8. Packet with unknown destination Bridge 1 Bridge 2 Bridging Loops

  9. Preventing Loops Packet with unknown destination FORWARDING FORWARDING FORWARDING BLOCKING

  10. Root Bridge A C B 3 1 2 4 D E F G 5 6 7 Symbols: H J I LAN 8 9 Bridge BLOCKING Spanning Tree Protocol

  11. Comparison of Source Route and Transparent Bridges • Transparent bridges are connection-less whereas source-route bridging provides connection-oriented networking. • Transparent bridges are completely invisible to the hosts and are fully compatible with all existing 802 products. • With Source-Route bridging, the network manager must manually install the LAN and bridge numbers. • One of the few advantages of source-route bridging is that, in theory, it can use optimal routing. • Source route bridges are more expensive, especially if they use VLSI chips in their interface cards. • Transparent bridges learn about bridge and LAN failures and other topology changes quickly and automatically.

  12. LAN Switches Switch HUB High Speed Backplane Each network device, for example, a file server, has dedicated bandwidth.

  13. HUB HUB HUB Switch HUB VLANs

  14. Advantages of Bridging • Bridges can connect networks running different protocols without requiring additional software. • Bridges form logically single networks. A bridge makes the movement of network devices, e.g. PCs, within the network easy. • Bridges are simple to install. • Bridges are cheaper than routers. • The presence of a bridge is transparent to users from the instant it is first installed, and bridges adapt automatically to network changes.

  15. Disadvantages of Bridging • Bridges cannot load-share traffic over two paths to a single destination, because the STA ensures that one of these paths will block all traffic. • Bridges cannot prevent a ‘broadcast storm’. • Bridges do not provide significant support for fault isolation or other distributed management capabilities.

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