bridge

A bridge is a data forwarding device that provides data transfer. You should understand the following concepts relating to the operation of bridges.

• Bridges connect two media segments that use the same protocol.
  Bridges examine the source address to determine the media segment of network devices.


• Bridges operate at the Data Link layer of the OSI model.


• Bridges maintain a table of device addresses and their corresponding segments.


• Each segment connected by a bridge can have the same network address.


• Messages within a media segment are prevented from crossing over to another segment.

Bridges' advantages:

• Bridges prevent wasted bandwidth by eliminating unnecessary traffic between segments.


• Bridges increase the maximum network length.


• Bridges forward packets for multiple upper-layer protocols.


• Bridges can link segments with dissimilar transmission media and media access methods.

Bridges' limitations:

• Bridges cannot link multiple architectures because different frame types are used.


• Bridges cannot translate upper-layer protocols.


• Bridges cannot forward packets to different networks based on the network address.


• Bridges do not filter broadcast packets.

Use bridges to isolate traffic to a segment, or to prevent unwanted traffic from crossing over to other segments, or to slow WAN links. When designing the placement of bridges on the network, follow the 80/20 rule.

• At least 80% of network traffic should stay within a segment.


• No more than 20% of network traffic should pass through the bridge to another segment.