QoS on egress traffic

[Nirmal Singh]

Hi All,

I having some doubts on whether QoS will be applied to egress traffic. Here's my scenario

Voice GW --->Core Sw-->WAN provider router

If calls are coming through to the Voice GW to say a Lync client, the traffic will be marked as dscp ef on the Voice GW and routed to the Core Switch. The Core Switch interface that's connected to the Voice GW is configured as mls qos trust dscp to trust whatever dscp marking on it.

The traffic is then routed out to the WAN provider router which then honours the marking and sets a bandwidth priority depending on the kind of dscp value.

My question is, do I need to configure any QoS on the interface on the Core Switch that's connecting to the WAN router for this egress packets?

Btw, the egress interface to WAN is a L3 routed interface whereas the interface on the Core Sw to the Voice GW is a L2 interface.

Please help

[andrew.butterworth]

The quick answer is yes but what you configure depends on the platform.  What is this 'core' switch?  If its a 3560 or 3750 then all you can achieve is egress queueing where you would typically enable egress expedite queueing  and map DSCP EF to this queue.  If its a 6500 with Sup720 then you can enable the same behaviour but you could also apply an egress QoS service policy (something you can't do on a 3560/3750).

Andy

[Joseph W. Doherty]

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Posting

My question is, do I need to configure any QoS on the interface on the Core Switch that's connecting to the WAN router for this egress packets?

It depends on whether this egress interface congests (i.e. packets queued for transmission) and whether such congestion, if any, delays packets enough that the network application's service requirements are not being met.  (NB: on high capacity/bandwidth links, queue drops might be a problem before actual queue delay.)