Why don the Catalyst 5000/6000 ATM modules bridge between two subinterfaces in the same virtual LAN (VLAN)?
A. The configuration guides for the ATM modules note the following restriction: If two PVCs are configured on the same VLAN and ATM module, packets received from one PVC are not forwarded to the other PVC. The reason has to do with the architecture of the modules. The WS-X515x series and the WS-X5166 use a unidirectional backplane interface chip that prevents the module from sending packets that it receives. The WS-X516x series uses two unidirectional backplane interface chips. However, it cannot send packets that it receives because of automatic echo suppression, which is enabled by default to avoid loops since the Spanning Tree logic in the Catalyst 5000 works per-port, per-VLAN and not on individual PVCs. The workarounds are: • Use a full-mesh rather than a hub-and-spoke ATM PVC design. • Use a router configured with the standard Cisco IOS bridging. You must configure two different subinterfaces in the same bridge group to allow broadcasts and other traffic to pass between two remot
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