Details the two packet classification systems used by the router to determine traffic marking and policy application. It compares the use of QoS maps and TCAM based on traffic direction and specific match conditions configured in the policy.
Your router uses two packet classification systems to determine traffic marking and policy application.
| Traffic direction |
Classification system |
|---|---|
| Ingress |
QoS map and Ternary Content Addressable Memory (TCAM) are used to classify incoming traffic. |
| Egress |
Only QoS map is used to classify outgoing traffic. |
Selection of classification system
Your router determines the classification system based on the match conditions you configure in the QoS policy.
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The router uses the QoS map when the policy matches on any of these fields:
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DSCP
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EXP
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PCP
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DEI
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QoS group
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If the match conditions do not include these fields, the router uses TCAM for classification.
Ternary Content Addressable Memory (TCAM) extends the concept of the Content Addressable Memory (CAM) table.
The table compares CAM and TCAM by match capabilities, use cases, and advantages in traffic classification.
| Attribute |
CAM |
TCAM |
|---|---|---|
| Match type |
Exact match (0 or 1) |
Ternary match (0, 1, or a wild card or “don’t care”) |
| Use case |
MAC address lookup, switch port mapping |
QoS policy classification, ACLs |
| Advantage |
Enables fast lookups for simple key-value queries |
Supports complex and flexible matching conditions |