Specifications

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Figure 29. Weighted Round Robin (WRR)

On the WS-X6248, 6148 and WS-X6348 line cards (with 2q2t queue structures), two transmit queues are used by

the WRR mechanism for scheduling. On the WS-X6548 line cards (with a 1p3q1t queue structure) there are 4 Tx

queues. Of these 4 Tx queues, 3 Tx queues are serviced by the WRR algorithm (the last Tx queue is a strict priority

queue). On GE line cards (except the 67xx cards), there are 3 Tx queues however (using a 1p2q2t queue structure);

one of these queues is a strict priority queue so the WRR algorithm only services 2 Tx queues. The WS-X67xx

series of GE linecards differ in that they offer 8 transmit queues of which one is a strict priority queue

Typically the administrator will assign a weight to the transmit queue. WRR works by looking at the weighting

assigned to the port queue, which is used internally by the switch to determine how much traffic will be transmitted

before moving onto the next queue. A weighting value of between 1 and 255 can be assigned to each of the port

queue.

Cat6500(config-if)# wrr-queue bandwidth 1 3

The above represents a three to one ratio between the two queues. You will notice that the Cisco IOS version of this

command applies to a specific interface only.

7.12 Egress ACL Support for Remarked DSCP

When a frame transits the switch, classification performed by the PFC can change the ToS priority setting (IP

Precedence or DSCP) in the packet. When the packet arrives at the egress port however, the default action will

result in the original ToS priority (not the PFC remarked ToS priority) that was present on the arriving packet to be

used for classification purposes.

Egress ACL support for remarked DSCP is supported by all members of the PFC3 family (including the PFC3A,

PFC3B and PFC3BXL). Any egress layer-3 port (either a routed port, or a layer-3 VLAN interface) can have this

feature applied to it. Enabling this feature on a port is achieved using the following command:

Cat6500(config-if)# platform ip features sequential