Table of Contents
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| Quality of Service
C
11
HAPTER
Creating QoS Policies
C
Q
S P
REATING
O
OLICIES
Use the Traffic > DiffServ (Configure Policy) page to create a policy map
that can be attached to multiple interfaces. A policy map is used to group
one or more class map statements
enforce bandwidth policing. A policy map can then be bound by a service
policy to one or more interfaces
Configuring QoS policies requires several steps. A class map must first be
configured which indicates how to match the inbound packets according to
an access list, a DSCP or IP Precedence value, or a member of specific
VLAN. A policy map is then configured which indicates the boundary
parameters used for monitoring inbound traffic, and the action to take for
conforming and non-conforming traffic. A policy map may contain one or
more classes based on previously defined class maps.
The class of service or per-hop behavior (i.e., the priority used for internal
queue processing) can be assigned to matching packets. In addition, the
flow rate of inbound traffic can be monitored and the response to
conforming and non-conforming traffic based by one of three distinct
policing methods as described below.
Police Flow Meter – Defines the committed information rate (maximum
throughput), committed burst size (burst rate), and the action to take for
conforming and non-conforming traffic.
Policing is based on a token bucket, where bucket depth (that is, the
maximum burst before the bucket overflows) is specified by the "burst"
field (BC), and the average rate tokens are removed from the bucket is
specified by the "rate" option (CIR). Action may be taken for traffic
conforming to the maximum throughput, or exceeding the maximum
throughput.
srTCM Police Meter – Defines an enforcer for classified traffic based on a
single rate three color meter scheme defined in RFC 2697. This metering
policy monitors a traffic stream and processes its packets according to the
committed information rate (CIR, or maximum throughput), committed
burst size (BC, or burst rate), and excess burst size (BE). Action may taken
for traffic conforming to the maximum throughput, exceeding the
maximum throughput, or exceeding the excess burst size.
The PHB label is composed of five bits, three bits for per-hop behavior,
◆
and two bits for the color scheme used to control queue congestion. In
addition to the actions defined by this command to transmit, remark
the DSCP service value, or drop a packet, the switch will also mark the
two color bits used to set the drop precedence of a packet for Random
Early Detection. A packet is marked green if it doesn't exceed the
committed information rate and committed burst size, yellow if it does
exceed the committed information rate and committed burst size, but
not the excess burst size, and red otherwise.
The meter operates in one of two modes. In the color-blind mode, the
◆
meter assumes that the packet stream is uncolored. In color-aware
– 294 –
(page
290), modify service tagging, and
(page
305).
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