Configuring Tail Drop - Cisco ASR 9000 Series Configuration Manual

Configuring Tail Drop

Command or Action
Step 10
exit
Example:
RP/0/RSP0/CPU0:router(config-pmap)# exit
Step 11
interface type interface-path-id
Example:
RP/0/RSP0/CPU0:router(config)# interface
gigabitethernet 0/2/0/0
Step 12 service-policy {input | output} policy-map
Example:
RP/0/RSP0/CPU0:router(config-if)#
service-policy output policy1
Step 13
commit
Configuring Tail Drop
Packets satisfying the match criteria for a class accumulate in the queue reserved for the class until they are
serviced. The queue-limit command is used to define the maximum threshold for a class. When the maximum
threshold is reached, enqueued packets to the class queue result in tail drop (packet drop).
The queue-limit value uses the guaranteed service rate (GSR) of the queue as the reference value for the
queue_bandwidth. If the class has bandwidth percent associated with it, the queue-limit is set to a proportion
of the bandwidth reserved for that class.
If the GSR for a queue is zero, use the following to compute the default queue-limit:
• 1 percent of the interface bandwidth for queues in a nonhierarchical policy.
• 1 percent of parent maximum reference rate for hierarchical policy.
Note The default queue-limit is set to bytes of 100 ms of queue bandwidth. The following formula is used to
calculate the default queue limit (in bytes):??bytes = (100 ms / 1000 ms) * queue_bandwidth kbps)) / 8
Restrictions
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide, Release
6.1.x
46
The parent maximum reference rate is the minimum of parent shape, policer maximum rate, and the
interface bandwidth.
Configuring Modular QoS Congestion Avoidance
Purpose
Returns the router to global configuration mode.
Enters the configuration mode and configures an interface.
Attaches a policy map to an input or output interface to be used as
the service policy for that interface.
• In this example, the traffic policy evaluates all traffic leaving
that interface.
• Ingress policies are not valid; the bandwidth and bandwidth
remaining commands cannot be applied to ingress policies.