Troubleshooting guide

12-3
ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Chapter 12 Troubleshooting Layer 2 Interfaces
Troubleshooting Layer 2 Switching
– Assign a port path cost on the outgoing interface (optional). When configuring POS uplink
interfaces and ATM uplink interfaces in conjunction with parallel Gigabit Ethernet links, we
recommend that you explicitly assign the port path cost to these interfaces because the default
value might not yield the optimal spanning tree.
Troubleshooting Layer 2 Switching
This section describes Layer 2 Switching troubleshooting and includes the following sections:
• Layer 2 Switching Broadcasts, page 12-3
• Troubleshooting Layer 2 Switching, page 12-5
• Other Layer 2 Switching Problems, page 12-10
• Layer 2 Bridging Troubleshooting Commands, page 12-12
Layer 2 Switching Broadcasts
Figure 12-1 shows the broadcast process all interfaces use to update all the other CAM tables in the
bridge group using the following processes:
• Each interface is the root of a P2MP VC.
• Leaves on all interfaces in the same bridge group are required to flood unknown unicast traffic
received on that port.
• Broadcasts VC setup when the interface is added to a bridge group.
• Each interface is a leaf of point-to-multipoint (P2MP) VCs, with roots on all other interfaces of the
bridge group.
Figure 12-1 Layer 2 Switching Broadcasts Used to distribute CAM Updates
Following is the process the switch uses to learn the MAC addresses as show in Figure 12-2:
1. Interface module microcode learns a new MAC Address
2. Interface module microcode sends an IPC to the route processor to update the bridging table
3. Aged entries are removed from the CAM
4. Interface module microcode sends an IPC to the route processor to remove the aged entry from
bridging tables
P2MP
leaves
P2MP
root
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