
ATM Features and Implementation Notes
5-11
Using Hybrid PVCs for Transparent Bridging
In Figure 5-6, traffic bridges between Site A and Site B. The bridge (Router 1) is
running on the ATM network interface, and its PVCs are not defined as
hybrid/bridged VCs.
Figure 5-6. Example of a Bridged Network
In this example, the bridge receives data from Site A. If the bridge does not
recognize the destination address, it tries to direct traffic through another bridge
port. However, since the PVCs are not defined as hybrid/bridged VCs, the ATM
bridge port views the paths to Site A and Site B as the same.
A bridge does not send out the same data over the bridge port from which it just
received the data. This means that the bridge cannot direct the data to Site B. To
resolve this problem, you need to designate the PVCs as hybrid/bridged VCs.
If you define the PVCs as hybrid VCs (refer to Figure 5-5), each PVC acts as a
separate bridge port. This enables the bridge running on the ATM interface to view
the traffic from Site A as arriving on a different port than that of Site B. When the
bridge sends out data, it now has access to all its ports, including the port that
accesses Site B. Therefore, data from Site A can reach Site B.
C
D
Router 1
B
A
Bridge port sees one
path to Sites A and B
Router 2
Router 3
E
F
ATM
Network
Site A Site B
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