QoS on Egress not supported? Huh?

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Aug 18th, 2007
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OK, if I have a switch with a whole bunch of IP phones connected to it and I want to ensure that the voice traffic is given priority queueing, dont I need to have that traffic classified and queued on the OUTPUT -- heading out to the WAN?

What good is QoS support on a switch if it doesnt support it on the egress, like the 3560?

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royalblues Sun, 08/19/2007 - 05:22
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First of all QoS should not be a concern at the LAN. The only thing that needs to be taken care is that the packets are properly marked ot trusted and presented the way you want when it hits the WAN router.

Campus congestion is a buffer & Queue management issue. Buffers can congest in LAN?s. QoS is required when there is congestion in buffers.This is when you mark the traffic and place types of traffic into different tranmit queues based on their priority

All the above things can be done on the 3560 switches



jwdoherty Sun, 08/19/2007 - 12:01
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"What good is QoS support on a switch if it doesn't support it on the egress, like the 3560?" Not much, if the 3560 didn't support egress QoS, but it does. For more information on QoS configuration for a 3560, see the relevant section of the configuration guide, e.g. http://www.cisco.com/en/US/products/hw/switches/ps5528/products_configuration_guide_chapter09186a008081db2f.html#wp1162303

For VoIP, consider defining an "expedited queue", for both input and output, and place such traffic there.

royalblues Sun, 08/19/2007 - 12:12
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The 3560 does not support egress service policies i.e it does not support the command service-policy output but only input under the interface or SVI.

The original poster is actually refering to the above case when he meant no egress qos support




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jwdoherty Sun, 08/19/2007 - 12:32
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Never stated that the 3560 supports outbound service policies.

Agreed that the original post was whether there's egress QoS support. Disagree with the statement that it doesn't offer any. The guide explains how to get such support, even if it's not using an outbound service policy.


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