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Packet Walk
page -34 OmniSwitch Troubleshooting Guide September 2005
Packet Walk
Packet Walk Principles
• All switching and routing is performed on the Ingress side of the switch. There are no address lookups
made on the Egress side.
• The Coronado combines the L2 switching and L3 routing logic into the same ASIC.
• Data always flows through the Nantucket even if the source and destination ports are on the same
Coronado.
• As indicated the “switching fabric” functionality is provided by Nantucket ASICs. The Nantucket
ASICs set also performs part of the broadcast/multicast processing by sending copies of multicast
packets to each Coronado in the system, and participates in the priority de-queuing logic.
Data Flow Overview
• Data flows in a 10/100 Mbps or Gigabit Ethernet port through the Catalina MAC ASIC and into the
Coronado ASIC.
• The Coronado’s HRE-X (Hardware Routing Engine) performs CAM (Content Address Memory) look-
ups on the source and destination addresses and selects a QID (queue ID) to switch the frame. The
queue selection is based upon L2 or L3 switching/routing criteria plus QoS priorities. The Coronado
ASIC can manage up to 2,048 queues. The Coronado could also queue up some frames for software
processing by the on-chip Sparc CPU for some specific unknown packets, which requires a particular
treatment.
• The Coronado’s Queue Manager then de-queues the frame from the appropriate queue based upon
destination and priority. The frame is output from the Coronado into the Nantucket switching fabric.
• The Nantucket provides minimal buffering and delivers the data to the destination Coronado for Egress
processing. Note that the destination Coronado can be the same Coronado or it can be different.
• The Coronado Egress processing sends the frame to the output port via the Catalina Ethernet inter-
faces. Notice that there is no CAM lookup processing or software processing during Egress. The Egress
processing logic also handles multicast processing in cooperation with the Nantucket.