C
HAPTER
37
| Quality of Service Commands
– 1180 –
COMMAND MODE
Policy Map Class Configuration
COMMAND USAGE
◆ You can configure up to 16 policers (i.e., class maps) for ingress ports.
◆ The
committed-rate
cannot exceed the configured interface speed, and
the
committed-burst
cannot exceed 16 Mbytes.
◆ Policing is based on a token bucket, where bucket depth (i.e., the
maximum burst before the bucket overflows) is by specified the
committed-burst
field, and the average rate tokens are added to the
bucket is by specified by the
committed-rate
option. Note that the
token bucket functions similar to that described in RFC 2697 and RFC
2698.
◆ The behavior of the meter is specified in terms of one token bucket (C),
the rate at which the tokens are incremented (CIR – Committed
Information Rate), and the maximum size of the token bucket (BC –
Committed Burst Size).
The token bucket C is initially full, that is, the token count Tc(0) = BC.
Thereafter, the token count Tc is updated CIR times per second as
follows:
■
If Tc is less than BC, Tc is incremented by one, else
■
Tc is not incremented.
When a packet of size B bytes arrives at time t, the following happens:
■
If Tc(t)-B ≥ 0, the packet is green and Tc is decremented by B down
to the minimum value of 0, else
■
else the packet is red and Tc is not decremented.
EXAMPLE
This example creates a policy called “rd-policy,” uses the class command to
specify the previously defined “rd-class,” uses the set phb command to
classify the service that incoming packets will receive, and then uses the
police flow command to limit the average bandwidth to 100,000 Kbps,
the burst rate to 4000 bytes, and configure the response to drop any
violating packets.
Console(config)#policy-map rd-policy
Console(config-pmap)#class rd-class
Console(config-pmap-c)#set phb 3
Console(config-pmap-c)#police flow 100000 4000 conform-action transmit
violate-action drop
Console(config-pmap-c)#
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