10-05-2007 07:39 AM - edited 03-03-2019 07:03 PM
Quick question on QoS:
If I have two Class-maps defined that overlap in their filtering, how is the priority handled? For example:
Class Map match-any VoIP
Match protocol rtp audio
Class Map match-any VideoConf
Match protocol rtp payload-type "4"
Match protocol rtp payload-type "34"
Am I correct that these two filters overlap since 'Match protocol rtp audio' is set to match Payload Types 0-23? If so, who would grab traffic that has the PT set to 4?
Thanks
10-05-2007 11:23 AM
I think it would depend how the policy was written. The policy that uses these classes would be processed in strict order.
Kevin Dorrell
Luxembourg
10-05-2007 12:56 PM
Thanks Kevin.
In strict order, do you mean in the order that the class-maps are entered under the Policy (as in top to bottom)? The Policy Map just marks the dscp and sets up the queue/bandwidth rules.
i.e.
policy-map Test
class VoIP
priority percent x
set ip dscp ef
class VideoConf
set ip dscp af41
bandwidth remaining percent xx
Based on this config, are you saying that class VoIP would be matched instead of VideoConf if a PT=4 came through because VoIP is listed first?
10-05-2007 02:19 PM
Hi,
NO, class voip is not matched first because of that , instead class voip is matched first because you are combining LLQ with CB/WFQ at your quing example.
LLQ is always matched first because it does contain priority Statment.
when acongestion occurs, the priority percent of the interface which alreay matching/classified by specific type of traffic are forwarded first out the egress queu till it reaches the maximum priority percentage specified, if still there is an extra priotrized traffic it just get dropped or mapped to the fair-qeue whenever there is no congestion.
After that , the CB/WFQ comes into the rule, the bandwidth statment gurantees a minimum bandwidth that could specific traffic gets whenever a congestion exist.
But always priotrized traffic matched first , which defines (Maximum bandwidth) of your voip traffic.
At the end, The rest of the traffic is then WFQ (Weighted fair queued) , as this treates all traffic fairly based on its usage.
HTH
Mohamed Sobair
10-06-2007 01:05 AM
Mohamed,
I think the Policy is executed strictly in the order the classes are defined under the policy i.e if the policy had been written as follows the rtp audio would be matched under the class VideoConf and not under voice
policy-map Test
class VideoConf
set ip dscp af41
bandwidth remaining percent xx
class VoIP
priority percent x
set ip dscp ef
Narayan
10-06-2007 01:52 AM
Narayan,
How is that? The class-map of VOIP is matching protocol rtp audio.
RTP Audio is not under (video-conf) class?
could you please explain your point further so that I can got it.
Regards,
Mohamed Sobair
10-06-2007 04:06 AM
Mohamed,
What i was trying to explain is that it is not necessary that the priority class would always be looked up first but it depends on the order of the class which are defined in the policy map.
If the same match parameters exists in two class maps, it will match the one that is reference first in the policy map
Narayan
10-06-2007 05:15 AM
Narayan,
Ok, However , this is applicable if the same match parameters exist right? if the Match prameters doesnt exist , still priority class will be forwarded 1st.
Regards,
Mohamed Sobair
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