Policy-Map Commands
12-96 Configuring Quality of Service
Syntax of the “no” Form
Thenoformofthiscommandsetstheconstanttothedefaultvalueof9:
no random-detect exponential-weighting-constant
Mode
PolicyMapClassconfiguration:XSR(config-pmap-c-<xx>)#
Example
ThefollowingexampleenablesWREDandsetstheweightconstantto(1/2)^5:
XSR(config)#policy-map wred
XSR(config-pmap<wred>)#class a
XSR(config-pmap-c<a>)#random-detect dscp-based
XSR(config-pmap-c<a>)#random-detect exponential-weighting-constant 5

random-detect precedence

ThiscommandsetsWeightedRandomEarlyDetect(WRED)theminimumandmaximum
thresholdandmaximumdropprobabilityvaluesforaIPprecedencevalue.
ThedefaultWREDmaximumdropprobability(MaxP)is1/10andthedefaultmaximumthreshold
(MaxTh)is40forallIPprecedencevalues.Thedefaultminimumthresholdiscalculatedfrom
MaxThbasedonfollowingformula:
MinTh=(1/2‐precvalue/16)xMaxTh
Tochangethedefaultsetting,usetherandom-detect precedence default command.Bydoing
so,allIPprecedencewillsharethesamevaluesexceptthosewhichwereexplicitlyconfigured
with random-detect precedence.ThissettingisusefulifWREDshouldoperateasRED.To
reverttotheoriginaldefaultsetting,enterno random-detect precedence default.
Syntax
random-detect precedence prec-value min-thres max-thres [mark-prob]default
Syntax of the “no” Form
ThenoformofthiscommandrevertsWREDparameterstothedefaultforaprecedencevalue:
no random-detect precedence prec-value
prec-value Precedencevalue,rangingfrom0to7withthekeyworddefault.
min-thres Minimumnumberofpacketsinthequeue,rangingfrom1to4096,
beyondwhichtheXSRrandomlydropspackets.
max-thres Maximumnumberofpacketsinthequeue,rangingfrom1to4096,
beyondwhichtheXSRdropsallpackets.
mark-prob Markprobabilitydenominator.Liklihoodofqueuedpacketstobe
droppedwhentheirnumberexceedingtheminimumlimitisbetween0
and(1/markprob).Range:1to65,536.