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cannot directly configure the DFC3x; rather, the master MSFC/PFC on the active supervisor controls and programs
the DFC.
The primary MSFC3 will calculate, then push down a FIB table (Forwarding Information Base) giving the DFC3x its
layer 3 forwarding tables. The MSFC will also push down a copy of the QoS policies so that they are also local to the
line card. Subsequent to this, local switching decisions can reference the local copy of any QoS policies providing
hardware QoS processing speeds and yielding higher levels of performance though distributed switching.
3.3 Linecard Port ASIC Queue Structure
The final aspect of QoS support in the Catalyst 6500 is implemented by ASIC’s (Application Specific Integrated
Circuits) on the linecard itself. Those ASIC’s implement the queues, buffering and threshold management used at
ingress and egress for the temporary storage of frames as they transit the switch.
Each of the ports on the linecards detailed below uses one of a number of specific queue structures. The queue
structures use nomenclature to indicate how many normal and strict priority queues are supported along with how
many thresholds per queue are available. The keywords in the queue structure type include the following:
●
“Q”—indicates the number of normal queues in the queue structure
●
“P”—indicates the number of Strict Priority (Low Latency) queues in the queue structure
●
“T”—indicates the number of thresholds per normal queue—the Strict Priority does not implement any form
of threshold.
Each of the queue structures in use on linecards today are listed in the table below and are further referenced in
each of the linecard sections that follow.
Table 2. Linecard Queue Structures
Queue Structure Receive or Transmit
Queue Type
Support Strict Priority
Queue
Number of Queues Number of Thresholds per
Queue
1Q2T Receive No 1 2
1Q4T Receive No 1 4
1Q8T Receive No 1 8
1P1Q0T Receive Yes 2 0
1P1Q4T Receive Yes 2 4
1P1Q8T Receive Yes 2 8
1P7Q2T Receive Yes 7 2
2Q8T Receive No 2 8
8Q8T Receive No 8 8
2Q4T Receive No 2 4
8Q4T Receive No 8 4
1P2Q2T Transmit Yes 3 2
1P3Q1T Transmit Yes 4 1
1P3Q4T Transmit Yes 4 4
1P3Q8T Transmit Yes 4 8
1P7Q4T Transmit Yes 7 4
1P7Q8T Transmit Yes 8 8
2Q2T Transmit No 2 2
Each of the major linecard groups are detailed below with a summary of the QoS features available for that linecard.