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

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

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. Source Route Bridging 2 3 1 4 5 6 7 8 Discovery Response

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

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

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

9. Preventing Loops FORWARDING BLOCKING FORWARDING Packet with unknown destination

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

13. VLANs Switch HUB

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.