Bridges are software based, while switches are hardware based because they use ASIC chips to help make filtering decisions.A switch can be viewed as a multi-port bridge. Switches have a higher number of ports than most bridges.Both bridges and switches forward layer 2 broadcasts. Bridges and switches learn MAC addresses by examining the source address of each frame received.Both bridges and switches make forwarding decisions based on layer 2 addresses. Three Switch Functions at Layer 2 Functions of layer 2 switching:
Layer 2 switches and bridges remember the source hardware address of each frame received on an interface, and they enter this information into a MAC database called a forward/filter table.
When a frame is received on an interface, the switch looks at the destination hardware address and finds the exit interface in the MAC database. The frame is only forwarded out the specified destination port.
If multiple connections between switches are created for redundancy purposes, network loops can occur. Spanning Tree Protocol (STP) is used to stop network loops while still permitting redundancy.
Loop Avoidance Spanning Tree Terms
Spanning Tree Operations
Root ID Priority 32769 Address 0005.74ae.aa40 Cost 19 Port 1 (FastEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address 0012.7f52.0280 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300
Root ID Priority 4097 Address 0012.7f52.0280 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 4097 (priority 4096 sys-id-ext 1) Address 0012.7f52.0280 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 15
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