QoS query on fair-queue command

[Santosh Shetty]

Old Cisco ios was supporting following commands for queuing.

class class-default
  set dscp default
  fair-queue 256
  queue-limit 128 packets
  random-detect

but new ios don't support   fair-queue 256, instead they have fair-queue queue-limit 128

do this new command will combine function of fair-queue 256  & queue-limit 128 packets

[rtnet_4820 · Accepted solution]

In Cisco new IOS like 15.1 the fair-queue command is hidden, so the default will be FIFO. But if you enable by typing the full command it overrides the default FIFO.

In new IOS if you use command "fair-queue queue-limit 128" that creates the number of queues as per the bandwidth of the interface and queue-limit defines the packets in each queue before it starts Tail drop.

This behaviour is same as in older IOS if you just enable the "fair-queue" and then define the queue-limit in each dynamically created queues.

[Cisco Freak]

What is fair queue?

CF

[rtnet_4820 · Accepted solution]

FQ is a dynamic scheduling method that provides fair bandwidth allocation to all network traffic. Routers maintain separate queues for packets from each individual source. The queues are serviced in Round-robin manner.

[Cisco Freak]

Got it. This is much better than FIFO.

Any restriction in the number of queue that can created?

CF

[rtnet_4820]

Santosh I mention this already in the comment before:

In new IOS if you use command "fair-queue queue-limit 128" that creates the number of queues as per the bandwidth of the interface and queue-limit defines the packets in each queue before it starts Tail drop.

For you reference again go to this site:

http://www.cisco.com/c/en/us/td/docs/ios/12_2/qos/command/reference/fqos_r/qrfcmd1.html#wp1097893

fair-queue (class-default)

To specify the number of dynamic queues to be reserved for use by the class-default class as part of the default class policy, use the fair-queue policy-map class configuration command

fair-queue [number-of-dynamic-queues]

 A power of 2 number in the range from 16 to 4096 specifying the number of dynamic queues. This when you want to define manually as per your scenario.