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Beginner

Traffic shaping and class priority

Hi,

 

If there is no traffic matched for class-audio,video and email, the limit default traffic can reach is 15Mbps? 

Can i say there are priority traffic shaping configured for class-audio,video and email?

How to check which class is higher priority?

But if there is no usage, the bandwidth can be used by other default traffic?

 

policy-map queuing
class audio
priority 3072
class video
bandwidth 3072
class email
bandwidth 8192
class class-default
policy-map limit
class class-default
shape average 15000000

4 REPLIES 4
Highlighted

Re: Traffic shaping and class priority

Hi,

 

If there is no traffic matched for class-audio,video and email, the limit default traffic can reach is 15Mbps? 

 

Yes, your understanding is correct.

 

Can i say there are priority traffic shaping configured for class-audio,video and email?

 

You configured Priority and bandwidth commands for different traffic classes. Both commands provide a bandwidth guarantee to the packets which match the criteria of a traffic class but there is a functional difference between these two commands.

 

Bandwidth command defines what is the minimum bandwidth reservation for a specific class when the network is congested.

 

Priority command defines what is the maximum bandwidth reserved for a specifc class when the network is congested.

 

Review the difference between these two commands from below:

 

https://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-packet-marking/10100-priorityvsbw.html

 

But if there is no usage, the bandwidth can be used by other default traffic?

 

during non-congestion, bandwidth can be used by any class. However, in your configuration for class-default your bandwidth will allways be shaped to 15000000

Highlighted
VIP Mentor

Re: Traffic shaping and class priority

Hello,

 

any unused bandwidth by the audio, video, and email classes can be used by the default class, so indeed if there is no traffic at all for these classes, the default class will shape up to 15MB.

 

The difference between the priority and the bandwidth is that the bandwidth has a minimum, but na maximum bandwidth guarantee, while priority has a maximum bandwidth guarantee and a built-in policer. So let's say the link is fully loaded, your audio class will get 3MB max, and video and email will get 3MB and 8MB respectively, at a minimum, and more if anything more is available.

 

Have a look at the link below:

 

https://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-packet-marking/10100-priorityvsbw.html

Highlighted
VIP Mentor

Re: Traffic shaping and class priority

Hello
At this time it looks like your two policy's are not nested so I would assume at present your just traffic shaping all traffic to 15mb thats if policy-map limit is appended to a egress interface such are you wan interface,for the child policy and it related class-maps to take affect the policy-map queuing  needs to be nested into the parent policy of policy-map limit which then need to applied to an interface
 
Lastly i would suggest you apply some fair queuing to the class default traffic

Example:
policy-map queuing
class class-default
fair queue

policy-map limit
class class-default
shape average 15000000
service-policy queuing

int x/x
description WAN
service-policy output limit 



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
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VIP Expert

Re: Traffic shaping and class priority

"If there is no traffic matched for class-audio,video and email, the limit default traffic can reach is 15Mbps? "

Correct. However, class-default limit is imposed by its shaper, the other classes don't matter, beyond assuming there's enough available bandwidth that the 15 Mbps limit can be obtained.

"Can i say there are priority traffic shaping configured for class-audio,video and email?"

No, LLQ is only defined for the audio class, as that's the only class with a priority statement.

"How to check which class is higher priority?"

First look if any classes are defined with the priority statement. Those classes have priority vs. all non-priority classes. Second, in later IOS variants, two levels of priority are supported. I recall priority 1 has priority over priority 2.

"But if there is no usage, the bandwidth can be used by other default traffic?"

Yes, but again, non-priority classes don't have priority against other similar classes (including those where bandwidth isn't defined). What happens with bandwidth defined classes is they obtain ratio based on their bandwidth statements. So, for example if both video and email wanted the same bandwidth, they would split it in the ratio of (about) 3072:8182.