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Example of Viewing Packet Classes Based on DSCP Value
!
policy-map-input input-policy
service-queue 1 class-map qos-BE1
service-queue 3 class-map qos-AF3
service-queue 4 class-map qos-AF4
trust diffserv fallback
!
class-map match-any qos-AF3
match ip dscp 24
match ip access-group qos-AF3-ACL
!
class-map match-any qos-AF4
match ip dscp 32
match ip access-group qos-AF4-ACL
!
class-map match-all qos-BE1
match ip dscp 0
match ip access-group qos-BE1-ACL
The packet classification logic for the configuration shown is as follows:
1. Match packets against match-any qos-AF4. If a match exists, queue the packet as AF4 in Queue 4, and if no match
exists, go to the next class map.
2. Match packets against match-any qos-AF3. If a match exists, queue the packet as AF3 in Queue 3, and if no match
exists, go to the next class map.
3. Match packets against match-all qos-BE1. If a match exists, queue the packet as BE1, and if no match exists, queue
the packets to the default queue, Queue 0.
4. You can optionally classify packets using their DSCP marking, instead of placing packets in Queue 0, if no match occurs. In
the above configuration, if no match occurs against match-all qos-BE1, the classification logic continues.
5. Queue the packet according to the DSCP marking. The DSCP to Queue mapping is as noted in Honoring dot1p Values on
Ingress Packets.
The behavior is similar for trust dot1p fallback in a Layer2 input policy map; the dot1p-to-queue mapping is noted in
Honoring dot1p Values on Ingress Packets.
To enable fall back to trust diffserve or dot1p, use the following command.
● Classify packets according to their DSCP value as a secondary option in case no match occurs against the configured class
maps.
POLICY-MAP-IN mode
trust {diffserve | dot1p} fallback
Mapping dot1p Values to Service Queues
All traffic is by default mapped to the same queue, Queue 0.
If you honor dot1p on ingress, you can create service classes based the queueing strategy in Honoring dot1p Values on Ingress
Packets. You may apply this queuing strategy globally by entering the following command from CONFIGURATION mode.
● All dot1p traffic is mapped to Queue 0 unless you enable service-class dynamic dot1p on an interface or globally.
● Layer 2 or Layer 3 service policies supersede dot1p service classes.
● Create service classes.
INTERFACE mode
service-class dynamic dot1p
Guaranteeing Bandwidth to dot1p-Based Service Queues
To guarantee bandwidth to dot1p-based service queues, use the following command.
Apply this command in the same way as the bandwidth-percentage command in an output QoS policy (refer to Allocating
Bandwidth to Queue). The bandwidth-percentage command in QOS-POLICY-OUT mode supersedes the service-class
bandwidth-percentage command.
● Guarantee a minimum bandwidth to queues globally.
Quality of Service (QoS)
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