Understanding the network.pdf - Back to Home

Bridges do forward traffic between network segments, and packet
forwarding is a function best performed as part of Layer 3 routing
process. In addition, the insertion of a bridge in an efficient
shared-medium LAN will result in slower network performance.
However, when they are properly applied, network bridges can be
used to improve traffic flow on a congested network. Switches can
attach shared-medium network segments to high-speed backbones
or interconnect remote networks running non-routable Layer 3
network protocols. There are three basic types of network bridges
used in LAN and WAN networking:
• Transparent bridges—These bridges are used to join network
segments that are based on the same Layer 2 protocol. Figure
6.2 illustrates the most common transparent bridge, an
Ethernet-to-Ethernet bridge.
Figure 6.2. A Ethernet-to-Ethernet bridge with
source address table (SAT).
• Translation bridges—These bridges are used to join network
segments that are based on different Layer 2 protocols. An
Ethernet-to-Token Ring bridge is an example of a translating
bridge. A variation on the translation bridge is the encapsulating
bridge, which is used to join networks that use the same Layer
2 protocol across a network that uses a different Layer 2