Giuseppe Larosa Mon, 05/31/2010 - 02:10
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Hello Manie,

this is a general requirement for QoS on multilayer switches.


Each frame or packet is associated with an internal QoS tag that by implementation choice is a DSCP field


As a result of this CEF is needed


To be noted in multilayer switches disabling CEF is  impossible they need it.


On SW based  routers almost all modern QoS tools require CEF to be enabled and even less recent tools like CAR, so it is not a surprise that CEF has to be enabled to support autoQoS


Hope to help

Giuseppe

Calin Chiorean Mon, 05/31/2010 - 02:22
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In addition to what Giuseppe said (which is actually a very good explanation) I want to add that AutoQoS is using NBAR to identify various applications and traffic types and CEF is requirement of NBAR.

If you look here:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/dtnbarad.htm#wp1050810

you'll see at Restriction, that NBAR does not support multicast and other non-CEF switching mode.

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