Bridge

Details about Bridge in Computer Network

1. BRIDGE R.RAMADEVI M.SC NS COLLEGE,THENI

2. Operate at the datalink layer Bridges use backward learning in recording sorurce address on transmissions Unlink repeaters dridges will not forward a frame on to another LAN segment if it knows about the location of the destination nodes Bridge management get move complicated when loop are possible in the frame route

3. Bridge are datalink layer connectivity devices that connect two or more LANs They are independent of the OSI upper layers They may be used to connect link network FOR EXAMPLE: Ethernet to Ethernet or tokerring T hey may be used to connect unlink network Ethernet to fddi Bridge use the MAC source and destination address to relay frames between connected network

4. Bridges have three basic functions: • Forwarding a frame from one segment to another across the bridge . • Filtering a frame that does not need to cross the bridge to reach its destination. • Flooding a frame to all ports when the location of the destination address is unknown. This lesson describes four types of bridges, transparent learning, translational, source route, and SRT bridges, including the primary algorithms employed by bridges to relay packets across a network.

5. Aging—Within the Spanning Tree algorithm, aging is the technique that allows addresses maintained in the forwarding table to be removed if they have not been accessed over a period of time. • Blocking—One of four Spanning Tree port states, blocking prevents a port from sending and receiving data. • Bridge Protocol Data Unit—BPDUs are the configuration messages used by bridges to calculate a Spanning Tree. • Flooding—When the forwarding table does not contain a Destination address for a station on a network, the bridge delivers the frame to all the interfaces on the network, except the interface (port) that received the frame.

6. Forwarding—A bridge is able to forward or relay a frame onto an interface by referring to its forwarding table of stored source addresses. • Interface—An interchangeable term for the port on an internetworking device. • Learning—One of four Spanning Tree port states, learning is an intermediary state when the bridge is building its forwarding tables. • Listening—During this Spanning Tree intermediary state, a port is listening to BPDUs and determines which bridge is the root and whether the port will go into the blocking or forwarding state.

7. Root bridge—Within the Spanning Tree algorithm, the root bridge has the lowest priority and MAC address and is responsible for maintaining a loop-free environment and for maintaining communication to other bridges in the network. • Route Discovery—The route discovery process is used in source-route bridging where the path from the source to the destination is discovered by receiving a pre-determined path documented inside the frame. • Routing Information Field—Used in source-route bridging, the RIF is a field placed just before the information field of a frame. The RIF contains a table of discovered paths including the ring and bridge number. Spanning Tree Algorithm—Bridges use the Spanning Tree Algorithm to ensure a loop-free topology by enabling a single path through the network.

8. TRANSPARENT LEARNING BRIDGE Digital Equipment Corporation developed the transparent learning bridge for transporting frames in an Ethernet network at the data link and physical layers of the OSI. Both the source and the destination have the same data link address format. The transparent learning bridge does not take part in route discovery or the route selection process. It does keep track of the location of each workstation on the network by building a forwarding table of each MAC address and the corresponding interfaces (ports) associated with each workstation.

9. SPANNING TREE ALGORITHM The Spanning Tree algorithm is a protocol developed by the IEEE to enable bridges to have multiple bridge connections between networks and reduce problems that occur from redundant links or loops in LANs . A maximum of eight bridges and seven active paths may exist between two devices using the Spanning Tree algorithm. The algorithm ensures a loop-free topology in a multi-bridge network.

10. BRIDGE C IS THE DESIGNATED BRIDGE FOR LAN 1 Blocking: The port is prevented from sending or receiving frames. Listening : The port is listening to BPDUs and determines Learning : The bridge forwarding table is being built while the port is listening. Forwarding:The port is allowed to receive or transmit frames.

11. Translational Bridges Translational bridges are a type of transparent bridge that connects LANs that use different protocols at the data link and physical layers, for example, FDDI and Ethernet . Source Route Bridges Source route bridging is used in token ring networks. A source route bridge links two or more rings together. There are fundamental characteristics in how a source route bridge transmits a frame between rings. A source route bridge does not create and maintain forwarding tables. The decision to forward or drop a frame is based on information provided in the frame.

12. SOURCE ROUTE TRANSPATENT BRIDGES (SRT) Source route transparent bridges are transparent bridges that combine the capabilities of the source route and the transparent bridge. When a SRT bridge receives a frame with a RIF, the bridge handles the frame just as a source route bridge would. If the bridge receives a frame without a RIF, it handles the frame the same as a transparent bridge would. Source Route Transparent bridges are commonly used in small token ring environments.

13. MACs WITH BRIDGE LOOP

14. MANs WITH BRIDGE LOOP

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