04-11-2011 06:23 AM - edited 03-04-2019 12:02 PM
Hi,
Anyone kind enough to explain this to me?
I have the configuration as below. I just would like to know the effect if let's say for example , class class-default. Current Bandwidth remaining is 25 percent of 2MB which is 0.5MB. So Let's say, there is traffic falls under this class which is more than 0.5MB but there isn't any traffic for video, will the traffic being restricted or it will still go through as there isn't any traffic for video which is 22 percent?
Hope some experts can enlight me on this. Thanks!
policy-map CBQ_2M
class class_Net_Critical
bandwidth remaining percent 6
queue-limit 64 packets
class class1-voice
priority 570
class class1-video
bandwidth remaining percent 22
queue-limit 128 packets
class class2-signalling
bandwidth remaining percent 6
queue-limit 64 packets
class class2
bandwidth remaining percent 31
queue-limit 75 packets
class class4
bandwidth remaining percent 6
queue-limit 64 packets
class class-default
bandwidth remaining percent 25
queue-limit 95 packets
policy-map shape_2M
class class-default
shape average 1900000 19000
service-policy CBQ_2M
!
Rgds,
KA
Solved! Go to Solution.
04-18-2011 07:47 PM
Hi Ken,
I think you're refering to the priority queue set at 670kbs
So if there's 400kpbs of traffic going through priority queue (PQ), the remaining 270kpbs would be shared amongst the other queues.
from the link
"
A. Yes. Although the bandwidth guarantees provided by issuing the bandwidth and priority commands have been described with words like "reserved" and "bandwidth to be set aside", neither command implements a true reservation. Meaning, if a traffic cla...
Do note the discussion about the PQ characteristics under congestion.
A great way to see how things behave in the real world is to run a few test. IPERF is a simple way of generating traffic between two PC's
HTH
Eugene
04-11-2011 06:53 AM
Hi, according to the Cisco QoS Exam certification guide, the scheduler gives a percentage of bandwidth to each class based on the configured values. If some queues do not need their bandwidth for a short period of time, then the bandwidth is spread across the other classes.
Please remember to rate all posts that are helpful.
04-11-2011 07:21 AM
Sean,
I will remember to rate the post if it is helpful.. :)
Just want to clarify more, when you say spread, is it mean by percentage as well? Let's say for the scenario above, There is no video traffic, how does it spread to other classes?
Thanks again!
KA
04-11-2011 10:31 PM
Ken,
According to the exam guide the actual workings of the scheduling algorithm for CBWFQ have not been published.
The only details available is that it provides a guarneteed bandwidth for each queue.
04-12-2011 01:18 AM
Hi Ken,
adding to Sean's point - remaining available bandwidth is allocated proportionally except in the case of the priority queue which is policed at the configured rate.
My favourite links for CBWFQ:
http://www.cisco.com/en/US/tech/tk543/tk545/technologies_q_and_a_item09186a00800cdfab.shtml
and
http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a0080103eae.shtml
They give pretty good examples.
HTH
Eugene
04-18-2011 04:45 AM
Eugene,
Thanks for your reply.
Let's say the Policy Queue 670kbps, and only 400kbps occupying the Class Voice, So can I say the balance of the packets 270Kbps would be able to utilise for other traffic or it is already Occupied for only class voice even though at certain time, 400kbps occupying the voice traffic only.
Thanks,
Regards,
KA
04-18-2011 05:11 AM
Hi Ken,
when there is no congestion the CBWFQ config doesn't apply.
When there is congestion and some traffic are not passing through then other class can use the bandwidth but Cisco doesn't tell how this is performed.
Regards.
Alain.
04-18-2011 07:47 PM
Hi Ken,
I think you're refering to the priority queue set at 670kbs
So if there's 400kpbs of traffic going through priority queue (PQ), the remaining 270kpbs would be shared amongst the other queues.
from the link
"
A. Yes. Although the bandwidth guarantees provided by issuing the bandwidth and priority commands have been described with words like "reserved" and "bandwidth to be set aside", neither command implements a true reservation. Meaning, if a traffic cla...
Do note the discussion about the PQ characteristics under congestion.
A great way to see how things behave in the real world is to run a few test. IPERF is a simple way of generating traffic between two PC's
HTH
Eugene
04-18-2011 09:15 PM
Thanks Eugene!
Have rated your post
04-19-2011 04:45 PM
Thanks Ken! Feel like pay day
Take care for now!
Eugene.
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