Quality of Service (QoS)
©2008 Allied Telesis Inc. All rights reserved.
39.18
AlliedWare Plus
TM
Operating System Software Reference C613-50003-00 REV E
Software Version 5.2.1
A surge of data exceeding the CIR will begin to empty bucket C. If bucket C empties to a point
where it has insufficient tokens to match to an incoming data packet, then the data packet will
be marked yellow. The data will now be measured against the level in bucket P and tokens will
be removed from this bucket to match the incoming data. If the incoming data rate drops to
less than the CIR then the data will continue to be marked yellow until the level in bucket C has
had a chance to fill, whereupon it will be marked
green
.
If the incoming data is greater than the PIR, then bucket P begins to empty. If bucket P empties
to a point where it has insufficient tokens to match to an incoming data packet, then the data
packet will be marked
red
. In this situation no tokens are removed from either bucket.
Note that although the data is metered per byte, the color marking process is applied per
packet. This means that if there were only sufficient tokens available to match part of a packet,
then the whole packet would be marked red. Then, depending on the
exceed action
parameter of the
police twin-rate exceed-action
command, the whole packet will be either
dropped, or marked and forwarded. In either situation, the red marked packet will leave the
bucket counts unchanged.
Configuring and Applying a Policer
The previous section showed how the policer works and how to select either the single rate or
twin rate exceed action. There are two methods to apply a policy to class maps.
1.
Select your policy-map and class-map from the command prompt, then enter either the
police twin-rate exceed-action
command or the
police twin-rate exceed-action
command whilst selecting the appropriate command parameters.
This will apply the command to the selected class-map. By running this command several
times, each for a different class-map, you can apply separate meter settings to each class-
map.
2.
Use the
mls qos aggregate-police exceed-action
to create a “named” aggregate policer
whilst whilst selecting the appropriate command parameters. Once you have done this,
you can use the
police aggregate
command to apply the aggregator to the policy-map and
class-map selected from the command prompt. Note that you cannot apply an aggregate
policer to a class map that has already been attached to a policer by using either the
police
twin-rate exceed-action
, or the
police twin-rate exceed-action
commands.
The main difference between these two methods is that you use method (1) to apply policing
to a number of class-maps, each having its own individually configured meter settings; whereas
you use method (2) to apply policing to a number of class-maps and police them all using a
single meter setting.
Note:
A set of class-maps that contribute traffic into a given aggregate policer can belong to
different policy-maps. This means that the aggregate policer can meter packets
destined for different egress ports.
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