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Policy-Map Commands
12-86 Configuring Quality of Service
Example
Thesecommandscreateclass‐mapclass1anddefineitsmatchcriteria:
XSR(config)#class-map class1
XSR(config-cmap<class1>)#match access-group 136
Thesecommandscreatethepolicymapwhichisdefinedtocontainpolicyspecificationsforclass1
andthedefaultclass:
XSR(config)#policy-map policy1
XSR(config-pmap<policy1>)#class class1
XSR(config-pmap-c<class1>)#bandwidth 2000
XSR(config-pmap-c<class1>)#queue-limit 40
XSR(config-pmap<policy1>)#class class-default
XSR(config-pmap-c<class-default>)#queue-limit 20
bandwidth
Thiscommandspecifiesormodifythebandwidthallocatedforaclassbelongingtoapolicymap.
Itisusedinconjunctionwithaclassdefinedbythe
class-mapcommand.Thebandwidth
commandspecifiesthebandwidthfortrafficinthatclass.Class‐BasedWeightedFairQueueing
(CBWFQ)derivestheweightforpacketsbelongingtotheclassfromthebandwidthallocatedto
theclass.CBWFQthenusestheweighttoensurethatthequeuefortheclassisservicedfairly.
Theamountofbandwidth
canbespecifiedinpercentagesorkilobitspersecond(kbps).When
configuredinkbps,theclassweightiscalculatedasaratioofthebandwidthspecifiedforthatclass
overtheavailablelinkbandwidth.Theavailablelinkbandwidthisequaltotheinterface
bandwidthminusthesumofallbandwidth
reservedforlowlatencyqueues.Whenconfiguredin
percentages,theclassweightisequaltothebandwidthpercentages.
Configuringbandwidthinpercentagesismostusefulwhentheunderlyinglinkbandwidthis
unknown,changesovertime,ortherelativeclassbandwidthdistributionsareknown.For
interfacesthathaveadaptiveshapingrates,
CBWFQcanbesetbyconfiguringclassbandwidthsin
percentages.
Thefollowingrestrictionsapplytothe
bandwidthcommand:
•Ifthe
percentkeywordisused,thesumofclassbandwidthpercentagescannotexceed100%.
•TheamountofbandwidthsetshouldbelargeenoughtoalsoaccommodateLayer2overhead.
•Apolicymapcanhavealltheclassbandwidthsspecifiedinkbpsoralltheclassbandwidths
specifiedinpercentages,butnota
mixofboth.But,theunitfortheprioritycommandinthe
priorityclasscanbedifferentfromthebandwidthunitoftheCBWFQ.
Syntax
bandwidth {bandwidth-kbps | percent percent}
Note: When the bandwidth of an interface is insufficient to satisfy the bandwidth of a policy map, the
interface becomes oversubscribed and some CBFWQ classes may become unable to transmit.
bandwidth-kbps
Amountofbandwidth,inkbps,assignedtotheclass.
percent
Availablebandwidthpercentageassignedtotheclass.