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QoS Using CBWFQ before reaching interface max bandwidth

CBWFQ kicks in when the interface becomes congested and there is no available space in the queue but I need to find a solution to the scenario below:

Im using a Gigabit interface on the 3945 Router that connects to the ISP. The ISP limits bandwidth to 60Mb so I need to make sure when I reach the limit of the 60Mb the router starts using the BW percentages defined in the policy-map using classes.

So, the idea is to let any kind of traffic go out as it wants but as soon as the 60Mb limit is reached, the priorities defined by the traffic classes will kick in just as if the interface ran out of queues (as CBWFQ usually works).

Have anyone implemented something like this?

Thanks for the help

7 REPLIES

QoS Using CBWFQ before reaching interface max bandwidth

Cisco IOS quality of service (QoS) offers two kinds of traffic regulation mechanisms—traffic policing and traffic shaping. A traffic policer typically drops traffic that violates a specific rate. A traffic shaper typically delays excess traffic using a buffer to hold packets and shapes the flow when the data rate to a queue is higher than expected.

You need to configure shaping at a rate of 60Mb.Here is a link describing the config tasks:

http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/percnt_polcng_shapng_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1026944

Also do not forget to configure the bandwidth on the interface appropriately i.e bandwidth 60000.

regards,

Leo

QoS Using CBWFQ before reaching interface max bandwidth

Jorge,

All what you need is actually define a (bandwidth 60000) command under the Gigabit interface, the QoS policy is triggered by this command to perform its Actions based on the type of queuing & claasses configured.

Regards,

Mohamed

New Member

QoS Using CBWFQ before reaching interface max bandwidth

Ok, so something like this would work?

The idea once again, let voice or web go out freely but if the total BW reaches 60Mb, then the bandwidth % defined in the classes will start to be used and queued respecting the %

So the shape command will lead to a congested state on interface. The subinterface then applies "backpressure," and Cisco  IOS begins queueing the excess packets that are held by the shaper???

class-map match-all WEB

  match access-group XXX

class-map match-all VOICE

match access-group XXX

!

policy-map QoS

class WEB

    bandwidth 25000

class VOICE

    bandwidth 35000

policy-map QoS-To-ISP

  class class-default

    shape average 60000000

    service-policy QoS

!
interface GigabitEthernet0/0
 bandwidth 61440
 service-policy QoS-To-ISP

Re: QoS Using CBWFQ before reaching interface max bandwidth

Just wanted to post a link to another thread on this:

https://supportforums.cisco.com/message/3432866#3432866

Looks like you already found the solution.

regards,

Leo

New Member

Re: QoS Using CBWFQ before reaching interface max bandwidth

Thanks but please confirm the main goal here:

"Let voice or web or whatever go out freely but if the total BW reaches 60Mb, then  the bandwidth % defined in the classes will start to be used and queued  respecting the %"

QoS Using CBWFQ before reaching interface max bandwidth

That is how it works.

You need the shaper to avoid ingress drops at the SP device because of policing.

QoS Using CBWFQ before reaching interface max bandwidth

There seems to be a lot of demand for info regarding qos.

This one might be useful for you as well:

https://supportforums.cisco.com/thread/2125467?tstart=0

regards,

Leo

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