Samsung Ubigate iBG3026, Configuration Manual

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Ubigate iBG3026 Configuration Guide/Ed.00
© SAMSUNG Electronics Co., Ltd.
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The ether-type value of 0x8847 is added to the hash table and a pointer to
class ‘mpls’ is stored in that entry. For any classification type, it is possible for
the match rule to have a range of values or multiple, non-contiguous values.
Remember that once the first child-class added and the ‘classification-type’ or
‘search-type’ is set in the parent class, any subsequent child classes of that
parent class must have the same classification type in its match rule.
Note that this is not a limitation but an inherent property of the hierarchical
classification concept.
For a given parent-class, if the search does not yield a match, the packet is
matched to the child-class pointed to by the ‘default_class’ attribute.
This class is known as a ‘default class’. One of the child-classes of a given
parent-class can be configured as a default class. If there is no default class,
packets for which the search does not yield a match will be dropped. In our
example, class ‘def’ is a default class of parent-class ‘root-out’. It would be
created as follows.
Configure/interface/bundle wan1/qos# add-policy-class def root-out
packetclass default
Each class has a queue structure associated with it. However, when a class
becomes a parent class due to the addition of child classes under it, its queue
structure ‘loses significance’ and is no longer active. The queue structure
plays major role in achieving CBQ queuing and scheduling.
Traffic Policing
Policing controls the traffic by dropping packets or marking down their
priority when the configured profile is exceeded. Shaping controls the traffic
by delaying packets using a queuing mechanism when they arrive faster than
the configured rate. Therefore shaping can smooth out the burstiness in a flow,
helping to minimize buffer overruns in intermediate routers. Policing does not
smooth out bursts, but it can control bursts by dropping packets or marking
them down.
Since shaping delays packets, thereby throttling the packet rate instead of
dropping them, adaptive applications(those using TCP) perform better.
Dropping packets can cause exponential back off of TCP, which can adversely
affect the throughput. This problem with policing can be minimized by
configuring the burst parameter of the policer to be a sufficiently large value.