06-29-2009 04:05 AM - edited 03-06-2019 06:30 AM
Hi,
I would like to verify that if there is a policy-map applied outbound in an interface whereby the policy-map looks something like this :-
Policy Map customer-x-out
Class voice
Class video
bandwidth 7000
Class gold
bandwidth 7000
Class silver
bandwidth 30000
Class control
bandwidth 2000
Class class-default
bandwidth 21000
that the service-policy only becomes in effect when there is congestion in the link ? If there is no congestion, then the policy-map does not come to effect. Would this be a correct statemet ?
Pls advice,
InternetB.
Solved! Go to Solution.
06-29-2009 04:10 AM
Correct. The policy map will only take effect when there is congestion on the link.
Jon
06-29-2009 04:10 AM
Correct. The policy map will only take effect when there is congestion on the link.
Jon
06-29-2009 11:29 AM
"If there is no congestion, then the policy-map does not come to effect. Would this be a correct statemet ? "
Yes, with regards to basic CBWFQ queuing. Not true if you were also using the CBWFQ policy to mark/police/shape packets (NB: as not done in your policy-map example).
"that the service-policy only becomes in effect when there is congestion in the link ?"
Keeping in mind above answer, logically yes, although even for basic policy queuing (such as your example) actually there's often an interface hardware queue or buffer, that when it overflows, the overflow packets are placed into the CBWFQ queue(s). I.e. some congestion might not derive benefit of your policy queuing. (NB: often interface command to adjust hardware queue/buffer size. Later IOSs are supposed to size default better.)
Also, policy maps can be used to manage queue congestion when the physical link isn't congested, such as for a subinterface or VC and/or under a shaper.
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