Dell Networking S6000 Uživatelský manuál stáhnout pdf (Strana 713)

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QoS rate adjustment is disabled by default.

• Specify the number of bytes of packet overhead to include in rate limiting, policing, and shaping

calculations.

CONFIGURATION mode

qos-rate-adjust overhead-bytes

For example, to include the Preamble and SFD, type qos-rate-adjust 8. For variable length

overhead fields, know the number of bytes you want to include.

The default is disabled.

Enabling Strict-Priority Queueing

Strict-priority means that Dell Networking OS de-queues all packets from the assigned queue before

servicing any other queues.

• The strict-priority supersedes bandwidth-percentage configuration.

• A queue with strict priority can starve other queues in the same port-pipe.

• Assign strict priority to one unicast queue.

CONFIGURATION mode

strict-priority

The range is from 1 to 3.

Queue Classification Requirements for PFC Functionality

Queue classification requirements for PFC functionality are mentioned below:

• On untagged ports, Queue classification must be based on DSCP.

• On tagged ports, Queue classification must be based on Dot1p. Layer 3 classification configurations

should not be present on the port.

• On hybrid ports, Queue classification can be based on either Dot1p (for tagged packets) or DSCP (for

untagged packets) but not both.

Example Case:

PFC does not work for tagged traffic, when DSCP based class map is applied on a hybrid port or on a

tagged port. Assume two switches A and B are connected back to back.

Consider the case where untagged packets arrive on switch A, if you want to generate PFC for priority 2

for DSCP range 0-7, then you have to match the interested traffic. You must use the class map and

associate to queue 1 using the policy map. The same class map needs to be applied in switch B as well

and when queue 1 gets congested, PFC would be generated for priority 2. Switch A on receiving PFC

frames with priority 2 would stop scheduling queue 1.

If a tagged packet with VLAN dot1p as 5 ingresses on switch A. Consider that tagged packet also has

DSCP in range of 0-7.These packets will match the class map and get queued on queue 1 on both the

switches.

Quality of Service (QoS)

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