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Earlier, when the priority of a queue at Per-Hop Behavior (PHB) was propagated all the way up the hierarchy towards the channel level, the PHB classes that had priority at PHB level would only be prioritized over other classes of subchannels. To avoid this, Priority Shaper feature is implemented.
Priory Shaper feature helps to balance the packet drops between the streams when multiple steams egress out of a priority queue. Egress QoS policy is supported on Priority Shaper.
Priority Shaper is supported only for PHB level classes.
Egress QoS Policy map with Priority Shaper can be applied only on the member interface of port channel and not at the logical level.
Policer configuration is not supported with the Priority Shaper configuration under same class map.
Priority Traffic Latency is increased during congestion with Priority Shaper configuration at Q level. Configure the queue limit with a lesser value for the priority queue to reduce the latency of priority traffic.
If the packet is from a 10G interface to a 1G interface, the bustiness is introduced. Due to this, dequeuing rate of this strict priority queue may be sometimes more than enqueuing. As a result, very few packet counters are seen in other queues.
Perform the following steps to configure Priority Shaper.
1.
enable
2.
configure terminal
3.
class-map
class-map-name
4.
match cos
number
5.
policy-map
policy-map-name
6.
class
class-map-name
7. priority level <level 1/2 > percent <percentage 1-100 > or priority level <level 1/2> <kbps> <burst size>
8.
interface
interface-type
interface-number
9.
service-policy output
policy-map-name
10. end
This section shows sample configurations for Priority Shaper.
Device(config)#class-map match-any class_level1 Device(config-cmap)#match cos 1 Device(config-cmap)#match cos 2 Device(config-cmap)#class-map match-any class_level2 Device(config-cmap)#match cos 3 Device(config-cmap)#match cos 4 Device(config-cmap)#class-map match-any class_bw Device(config-cmap)#match cos 5 Device(config-cmap)#end . Device(config)#policy-map shape_priority Device(config-pmap)#class class_level1 Device(config-pmap-c)#priority level 1 per 10 Device(config-pmap-c)#class class_level2 Device(config-pmap-c)#priority level 2 per 20 Device(config-pmap-c)#class class_bw Device(config-pmap-c)#bandwidth remaining percent 70 Device(config-pmap-c)#end Device(config)#interface GigabitEthernet0/0/3 Device(config-if)#load-interval 30 Device(config-if)#service-policy output shape_priority Device(config-if)#end
Note | The match cos is not supported at egress on the Cisco RSP3 Module. |
Device# show policy-map interface TenGigabitEthernet0/0/2 show policy-map interface TenGigabitEthernet0/0/2 TenGigabitEthernet0/0/2 Service-policy output: shape_priority queue stats for all priority classes: Queueing priority level 1 queue limit 3932 us/ 49152 bytes (queue depth/total drops/no-buffer drops) 49476/44577300/0 (pkts output/bytes output) 2348138/1202246656 queue stats for all priority classes: Queueing priority level 2 queue limit 1966 us/ 49152 bytes (queue depth/total drops/no-buffer drops) 51072/42228358/0 (pkts output/bytes output) 4697080/2404904960 Class-map: class_priority (match-any) 46925438 packets, 24025824256 bytes 30 second offered rate 1871849000 bps, drop rate 1778171000 bps Match: cos 1 Match: cos 2 Priority: 10% (100000 kbps), burst bytes 2500000, b/w exceed drops: 44577300 Priority Level: 1 Class-map: class_priority_level2 (match-any) 46925438 packets, 24025824256 bytes 30 second offered rate 1871849000 bps, drop rate 1684485000 bps Match: cos 3 Match: cos 4 Priority: 20% (200000 kbps), burst bytes 5000000, b/w exceed drops: 42228358 Priority Level: 2 Class-map: class_bw (match-any) 23462719 packets, 12012912128 bytes 30 second offered rate 935925000 bps, drop rate 281045000 bps Match: cos 5 Queueing queue limit 393 us/ 49152 bytes (queue depth/total drops/no-buffer drops) 49476/7045085/0 (pkts output/bytes output) 16417634/8405828608 bandwidth remaining 70% Class-map: class-default (match-any) 0 packets, 0 bytes 30 second offered rate 0000 bps, drop rate 0000 bps Match: any queue limit 393 us/ 49152 bytes (queue depth/total drops/no-buffer drops) 0/0/0 (pkts output/bytes output) 0/0