question on bc value for CB policing

From: nagendra kumar (nagendranainar@yahoo.co.in)
Date: Wed Apr 09 2008 - 04:37:57 ART


Hi All,
  
  I am aware that with policing, the token refilling will happen based on the time elapsed between packets being policied. So for a link configured with a police rate of 1 Mbps, the number of token added after 1 second elapsed between packet will be 1Mbps/8. Now the Bc value is the one which decides the size of the token bucket
  
  Having both the points in mind, if we configure the below command,
  
  policy-map TEST
    class class-default
    police cir 1000000 bc 1000
      exceed-action drop
  
  ###sh policy-map int e0/0.20
   Ethernet0/0.20
  
    Service-policy input: TEST
  
      Class-map: class-default (match-any)
        2 packets, 156 bytes
        5 minute offered rate 0 bps, drop rate 0 bps
        Match: any
        police:
            cir 1000000 bps, bc 1000 bytes
          conformed 2 packets, 156 bytes; actions:
            transmit
          exceeded 0 packets, 0 bytes; actions:
            drop
          conformed 0 bps, exceed 0 bps
  
  As per the above configuration, the police rate is 1 Mbps and after 1 second time elapsed, it is suppose to fill 125000 (1Mbps/8) tokens to the bucket which is capable of storing only 1000 tockens. So shouldn't the router throw an error mesage, if the Bc value is less than PoliceRate/8 value?.
  
  Also the default value of Bc is PolicaeRate/32. So if the PoliceRate is 1Mbps, the default Bc value will be 31250 which makes the token bucket of size less than 125000 tokens.
  
  Am I missing something here?...
  
  Regards,
  Nagendra
  
  
  
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