Troubleshooting guide
11-18
ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Chapter 11 Troubleshooting Layer 3 Network Connections
System Architecture
engine completes the lookup, the packet moves from internal memory into the frame FIFO buffer. In
parallel, the search engine returns to the control FIFO buffer all of the relevant rewrite and QoS
information.
The Fabric Interface then rewrites the packet with the appropriate information and calculates the
checksum. At the same time, the Fabric Interface adds to the beginning of the packet the internal routing
tag containing port of exit, the QoS priority, and drop priority (see Figure 11-8). Once completed, the
Frame Scheduler is signaled to place the frame into the fabric.
At the output port, the Fabric Interface forwards the packet to its output MAC. Since all rewrite and error
checking has been done at the ingress port, no additional work needs to be performed on that frame.
Private, Shared, and Dual CAMs
Private CAM describes where each interface has its own CAM. The CAM space is used to store direct
lookup tables, Layer 2 and Layer 3 forwarding tables that assist in the ASIC hardware forwarding. See
Figure 11-12.
The various CAM types are described as follows:
• Private CAM
–
Each FastEthernet interface has its own CAM space
–
1-to-1 ratio between hardware interface and CAM
• Shared CAM
–
One Ethernet processor interface (4 Ports) share CAM Space
–
1-to-many ratio between hardware interface and CAM
• Dual CAM found on current Gigabit Ethernet module
–
One CAM per Ethernet processor interface (2 Ethernet processor interfaces per Gigabit Ethernet
processor interface)
–
Many-to-1 ratio between hardware interface and CAM
Figure 11-12 Private CAM
The shared CAM allows one single CAM space per Ethernet processor interface, and this CAM space is
physically shared among all four ports within this interface. See Figure 11-13. Shared CAM space has
implications in the way the direct lookup table and Layer 3 database are maintained in the CAM.
14K/62K CAM
Entries per port
2K Interface
table
14K/62K CAM
Entries per port
14K/62K CAM
Entries per port
14K/62K CAM
Entries per port
2K Interface
table
2K Interface
table
2K Interface
table
(S1, G1) (S1, G1) (S1, G1) (S1, G1)
Port 0 Port 1 Port 2 Port 3
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