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Understanding QoS Configuration on the Matrix N-Series
Priority: For each new CoS index created, you have the option to assign an 802.1p priority value
0‐7 for the class of service. CoS indexes 0‐7 map directly to 802.1p priorities and cannot be changed
as they exist for backward compatibility. All other CoS index entries can have a priority value set
between 0 and 7.
ToS: The IP header Type of Service field is an 8‐bit field also referred to as the DiffServ Code Point
(DSCP) field. This optional value can be set per class of service to a value between 0–255. When a
frame is assigned to a class of service for which this value is configured, the ToS field of the
incoming IP packet will be overwritten to values defined by you. This ToS rewrite option also
allows masking. The ToS can selectively mask (change) certain bits of the field, without changing
others. For instance masking the ToS could be used to modify the ToS precedence without
modifying the DTR/ECN bits. The mask specified contains the bits to be changed. CLI input can be
in decimal or hex value, and a mask is not required. If the mask is not specified in the ToS input, all
bits will be overwritten. ToS can be set for CoS indexes 0‐7.
TxQ Reference: Because all traffic requires association to a transmit queue, the CoS TxQ reference
field will always be populated when a new CoS index is created. If a TxQ reference value is not
chosen, TxQ reference 0 will be assigned. The reference does not indicate the actual transmit
queue to be assigned by CoS; it points to the CoS TxQ Reference Mapping Table Index entry. It
may be thought of as the virtual queue that is associated to a physical queue defined by the TxQ
Reference Mapping Table. TxQ Reference Mapping Table defines 16 TxQ references, therefore CLI
input for TxQ reference in the CoS Settings Table is 0‐15. See "CoS TxQ Reference Mapping" on
page
15 for a TxQ reference configuration discussion.
IRL Reference: The CoS IRL reference field is optional, as rate limits are not required. Like the
TxQ reference field, the IRL reference does not assign an inbound rate limit but points to the CoS
IRL Reference Mapping Table. This reference may also be thought of as the virtual rate limiter that
will assign the physical rate limiter defined by the IRL Reference Mapping Table. The IRL
Reference Mapping Table defines 32 IRL references, therefore input for IRL reference in the CoS
Settings Table is 0‐31. See "CoS IRL Reference Mapping Table" on page
configuration discussion.
New CoS Indexes can be created using the set cos settings command. ToS, 802.1p priority, TxQ
reference, and IRL Reference can be configured for each CoS Index. You need to:
•
Enter a CoS Index value from 0–255
•
Specify 802.1p priority (Index entries 8–255 only), tos‐value, txq‐reference and irl‐reference
Use the set cos settings command to create or modify an already existing CoS index.
Use the show cos settings command to display current CoS indexes.
February 22, 2008
17 for an IRL reference
Page 18 of 29
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