BRIDGE

Bridge – A bridge operates at data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LAN's working on the same protocol. It has a single input and single output port, thus making it a 2 port device.

Types of Bridges

• Transparent Bridges:- These are the bridge in which the stations are completely unaware of the
  bridge’s existence i.e. whether or not a bridge is added or deleted from the network, reconfiguration of
  the stations is unnecessary. These bridges make use of two processes i.e. bridge forwarding and bridge learning.
• Source Routing Bridges:- In these bridges, routing operation is performed by source station and the frame specifies which route to follow. The hot can discover frame by sending a special frame called discovery frame, which spreads through the entire network using all possible paths to destination.
• Multi port Bridge:-A multi port bridge connects multiple networks and operates transparently to decide on a frame-by-frame basis whether to forward traffic. Additionally, a multi port bridge must decide where to forward traffic. Like the simple bridge, a multi port bridge typically uses store and forward operation. The multi port bridge function serves as the basis for network switches.
• Implementation:-The forwarding information base stored in content-addressable memory (CAM) is initially empty. For each received ether net frame the switch learns from the frame's source MAC address and adds this together with an ingress interface identifier to the forwarding information base. The switch then forwards the frame to the interface found in the CAM based on the frame's destination MAC address. If the destination address is unknown the switch sends the frame out on all interfaces (except the ingress interface). This behavior is called uni cast flooding.