Cisco Nexus 9000 Series Configuration Manual page 110

Approximate Fair Drop
AFD User Profiles
Three user profiles are provided with AFD:
• Mesh (Aggressive)
AFD and ETRAP timers are set to be aggressive, so that the queue depth does not grow much and is
kept close to the queue-desired value.
• Burst (Default)
AFD and ETRAP timers are neither aggressive nor conservative, so that the queue depth could be
observed to be hovering near the queue-desired value.
• Ultra-burst (Conservative)
AFD and ETRAP timers are set to be conservative, so that more bursts are absorbed and fluctuations
for queue depth can be observed around the queue-desired value.
These profiles set the ETrap and AFD timers to pre-configured values for different traffic profiles such as,
very bursty or not-so bursty traffic. For more configuration flexibility, the ETrap period set by the profile can
be overridden by configuring the ETrap age-period with the hardware qos etrap command. However, the
AFD timer cannot be changed.
The following is an example of configuring the ETrap age-period:
switch(config)# hardware qos etrap age-period 50 usec
The following are examples of configuring the AFD user profiles:
• Mesh (Aggressive with ETrap age-period: 20 µsec and AFD period: 10 µsec)
switch(config)# hardware qos afd profile mesh
• Burst (Default with ETrap age-period: 50 µsec and AFD period: 25 µsec)
switch(config)# hardware qos afd profile burst
• Ultra-burst (Conservative with ETrap age-period: 100 µsec and AFD period: 50 µsec)
switch(config)# hardware qos afd profile ultra-burst
WRED and AFD Differences
Although WRED and AFD are both AQM algorithms, they have different approaches to help manage
congestion:
• WRED computes a random drop probability and drops the packets indiscriminately across all the flows
in a class of traffic.
• AFD computes drop probability based on the arrival rate of incoming flows, compares it with the
computed fair rate, and drops the packets from the elephant flows while not impacting the mice flows.
AFD and WRED cannot be applied at the same time. Only one can be used in a system.
Note
Cisco Nexus 9000 Series NX-OS Quality of Service Configuration Guide, Release 7.x
96
Configuring Queuing and Scheduling