VoIP QoS

Answered Question
Apr 11th, 2007
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This is the QoS i have configured on the router to give priority for VoIP


My VoiP subnet is 172.20.92.0/25


This is the following QoS i have


class-map match-all voice

match access-group name voice

match ip dscp ef

!

!

policy-map WAN

class voice

priority 768

class class-default

fair-queue


ip access-list extended VOICE

permit udp 172.20.92.0 0.0.0.127 any range 16384 32767


I do not see any packets that match the voice policy nor the access-list.


Is there any change required in the access-list?


Narayan

Correct Answer by paul_alexander about 10 years 3 months ago

Yeah you could mark the traffic ingress to the router and then just match dscp and prioritise egress over the WAN.


What kind of switch do you have? Its most likely that if its not configured to trust the IP phones, it will by default strip the markings of anything it receives.












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paul_alexander Wed, 04/11/2007 - 01:13
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Hi Narayan,


Your acccess list name and the match statement on the class-map are case sensitive.


Make them both lower or upper case and you should see maches.


Another thing you should make sure of is that your voice packets are actually being marked with dscp ef. Your class-map is a "match-all" so even if the access list is being matched, unless the packets are marked with dscp ef, it still wont work.




Cheers,


Paul.


royalblues Wed, 04/11/2007 - 01:28
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Paul,


Thanks i never realised that i have used capslock while configuring the access-list.

Will modify it accordingly


I thought the cisco Ip phone automatically sets it to DSCP EF and cos 5.


Narayan


regards

Narayan


paul_alexander Wed, 04/11/2007 - 01:29
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Yep, by default it does. But its also possible that it could be stripped somewhere before it hits the router.


It may not be happening. But its something to be aware of :)


Paul.


royalblues Wed, 04/11/2007 - 01:51
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Paul,

Still no hits on the policy map after changing the access-list.

I am getting hits on the access-list which ensures the access-list is correct


I think the dscp is getting stripped somewhere.

Is there any other way to check other than sniffing the traffic?


Would it be a better way to have the access-list on the L3 before the Wan router and set it explicitly.


ip access-list extended voice

permit udp 172.20.92.0 0.0.0.127 any range 16384 32767


class-map match-all voice

match access-group name voice


policy-map MPLS

class voice

set ip dscp ef


Narayan

Correct Answer
paul_alexander Wed, 04/11/2007 - 01:59
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Yeah you could mark the traffic ingress to the router and then just match dscp and prioritise egress over the WAN.


What kind of switch do you have? Its most likely that if its not configured to trust the IP phones, it will by default strip the markings of anything it receives.












royalblues Wed, 04/11/2007 - 02:57
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the switches i have in that site are 2960's at the access which connect to a 3750 core to which the wan router is connected.


should trusting the switch only on the trunks help or should it be done on each port where the phone connects. Users keep moving the phone from one point to another


Narayan

royalblues Wed, 04/11/2007 - 03:20
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Paul,


Actually somebody had configured autoqos on the switches and was trustung the COS value from the phone and not the DSCP.


I configured the ports to trust the DSCP and it started working.


Narayan

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