Unanswered Question
Sep 10th, 2007


If we are configuring QoS and applying the policy on the WAN interface, is it necessary to have the same policy at both A and Z ends of the WAN link??

Please suggest.



I have this problem too.
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navneet_78 Mon, 09/10/2007 - 07:49

WOuld appreciate if someone would reply to my Query.



Kevin Dorrell Mon, 09/10/2007 - 07:56

No, it is not necessary. But it rather depends on what you have in the policy, and what you are trying to achieve. If you are shaping or policing traffic, then it makes sense to do so on transmission.

You can shape a transmission, but not a reception. You can police on transmission or reception, but if you have the option it makes more sense to do so on the transmitting end cos that way the dropped packets are not consuming your valuable bandwidth.

Furthermore, you can have different policies in each direction if you really want.

Perhaps if you tell us more about what you are trying to achieve, we can give more helpful guidance.

Kevin Dorrell


navneet_78 Mon, 09/10/2007 - 08:04

Thnx for your reply Kevin!!

I need to make sure in my environment, that Voice (Telepresence) is given more preference over other traffic.

I have configured QoS on my primary WAN-GW (E3 link) for supporting voice traffic like Telepresence. I have a backup with 2 E1s on GW2 device.

Iam wondering if i need to apply the same backup-Qos on both ends on the GW2??

Since this is voice specific traffic, I need to make sure the packets flowing from the Z end also get the proper QoS..right? That means I should use the same QoS on both ends?



cisco_lad2004 Mon, 09/10/2007 - 09:16

Hi Navneet

1- u need to apply QOS on both primary and backup interfaces.

2-depending on what you are doing with QOS:

a-if u are marking Voice traffic oubound, u do not need to remark in on next router inbound. as it is already marked.

b-if u are classifying traffic and putting it in a priority Q, all routers in teh voice traffic path needs to support same strategy.

so in short, u mark voice at ingress only. then u apply the VIP treatment in every device along the path.

Traffic returning, is basically ingressing for the opposite direction, so yes you remark it and apply same VIP treatment.



navneet_78 Tue, 09/11/2007 - 00:26

Hey Sam,

Thanks for ya reply.It really was very helpful..


Kevin Dorrell Mon, 09/10/2007 - 22:57


Yes, in this case you would apply QoS at both ends of the link, in each case to prioritise the traffic going out onto the line.

As a previous post has suggested, you should mark the traffic as close as possible to its source. Althogh the queuing policies are applied on a hop-by-hop basis, it is always a good idea to take an end-to-end view of the QoS.

Depending on your queueing policy, and how it is expressed, you might want to adapt it for the lower bandwidth of the E1 lines. The QoS will be more critical on the E1s than on the E3 because the E1s are more likely to become congested.

Kevin Dorrell



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