The CoS settings table assigns a priority, a ToS value, TxQ reference table and an IRL reference to a CoS entry as follows:
CoS Index - Indexes are unique IDs for each CoS settings table entry. CoS indexes 0–7 are created by default and mapped directly to an 802.1p priority values 0–7 for backwards compatibility. These entries cannot be removed and the 802.1p value cannot be changed. When CoS is enabled using the set cos state enable command, indexes are assigned. Entries 0–255 are configurable for a total of 256 CoS entries.
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 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 for an IRL reference configuration discussion.
ORL Reference (S-, K-Series): The CoS ORL reference field is optional, as rate limits are not required. Like the TxQ and IRL reference fields, the ORL reference does not assign an outbound rate limit but points to the CoS ORL 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 ORL Reference Mapping Table. The IRL Reference Mapping Table defines 48 ORL references, therefore input for ORL reference in the CoS Settings Table is 0 - 47. See CoS ORL Reference Mapping Table (S-, K-Series) for an ORL reference configuration discussion.
Drop-Precedence Reference (S-, K-Series): Drop-Precedence indicates a preference for dropping packets, often used in association with Weighted Random Early Detection (WRED) queues. The S- K- and 7100-Series implementation uses the values to prioritize packets. Drop precedence has a special meaning within a Flex-Edge context. Packets assigned a drop-precedence value are assigned a 4th level of priority in the Flex-Edge mechanism, and are limited to rules applied to a single port. See Flex-Edge (S-, K-Series) for a detailed Flex-Edge drop-precedence discussion.
Flood Control Reference: The CoS flood control reference field is optional. Flood control limiting is not required. Enable or disable flood control for the specified CoS index.
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:
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.
The following example displays default values for the show cos settings command S-Series output (S-, K-Series):
System(rw)->show cos settings * Means attribute has not been configured CoS Index Priority ToS TxQ IRL ORL Drop Prec Flood-Ctrl --------- ---------- ------- ----- ----- ----- --------- ---------- 0 0 * 0 * * * Disabled 1 1 32.0 4 * * * Disabled 2 2 64.0 8 * * * Disabled 3 3 96.0 12 * * * Disabled 4 4 128.0 16 * * * Disabled 5 5 * 10 11 * * Disabled 6 6 * 12 * * * Disabled 7 7 * 14 * * * Disabled
The following example displays default values for the show cos settings command 7100-Series output:
System(rw)->show cos settings * Means attribute has not been configured CoS Index Priority ToS TxQ IRL Flood-Ctrl --------- ---------- ------- ----- ----- ---------- 0 0 * 0 * Enabled 1 1 * 1 * Enabled 2 2 * 2 * Enabled 3 3 * 3 * Enabled 4 4 * 4 * Enabled 5 5 * 5 * Enabled 6 6 * 6 * Enabled 7 7 * 7 * Enabled
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