|| Select the
Classification Profile (class map) and define the actions to be applied if
traffic matches the profile. You can define Policing, Marking, Queuing,
Shaping, RED actions, and Service Policy (H-QoS). There is a tab for each of
these action types and its definitions, as follows:
Traffic policing manages the maximum rate of
traffic allowed on an interface through a token bucket algorithm. Traffic
policing also provides a certain amount of bandwidth management by allowing you
to set the burst size (Bc) for the CIR. When the peak information rate (PIR) is
supported, a second token bucket is enforced and this two-rate policer can
meter traffic at two independent rates: the committed information rate (CIR)
and the peak information rate (PIR). The committed token bucket can hold bytes
up to the size of the committed burst (bc) before overflowing and determines
whether a packet conforms to or exceeds the CIR. The peak token bucket can hold
bytes up to the size of the peak burst (Be) before overflowing, and determines
whether a packet violates the PIR. Different actions can be taken if a packet
conforms, exceeds, or violates the CIR/PIR. For instance, packets that conform
can be configured to be sent, packets that exceed can be configured to be sent
with a decreased priority, and packets that violate can be configured to be
Policer Action tab, specify the following:
Committed Information Rate (CIR)—The long-term average transmission rate, specified in bits per second (bps) or as a percentage of the available or unused bandwidth. Traffic that falls under this rate will always conform. Ensure that the CIR value you enter is supported on the device and choose the right CIR unit value (bps, kbps, mbps, gbps, or percent).
(Bc)—How large traffic bursts can be (in bytes) before some traffic exceeds the
Peak Information Rate (PIR)—How much traffic bursts can peak before some traffic exceeds the PIR value associated with the CIR. Ensure that the PIR value you enter is supported on the device and choose the same unit value you chose for CIR (bps, kbps, mbps, gbps, or percent).
Burst (Be)—How large traffic bursts can be (in bytes) before traffic exceeds
Under Traffic Coloring Behaviour, select the action to be performed if the traffic conforms, exceeds, or violates the rate limit. Provide values as required. To enable color-aware traffic policing specify the Conform Color and Exceed Color values by associating them with respective class profiles. With color-aware policing, the following results occur based on the CIR, the PIR, and the conform actions, exceed actions, and violate actions:
Packets that have metering rates less than or equal to the CIR and belong to the specified class (conform-color) are policed as conforming to the rate. These packets are also policed according to the conform action specified. In this instance, the packets will be transmitted.
Packets that have metering rates between the CIR and the PIR and belong to either to the conform-color class or exceed-color class are policed as exceeding the CIR. These packets are also policed according to the exceed action specified. In this instance, the precedence value of the packets will be set and the packets transmitted.
Packets that have metering rates higher than the PIR or belong to neither class conform-color or class exceed-color are policed as violating the rate. These packets are also policed according to the violate action specified. In this instance, the packets will be dropped.
Marker Action: Packet marking allows you to
partition your network into multiple priority levels or classes of service.
Marking of a traffic flow is performed by:
Setting IP Precedence or DSCP bits in the IP Type of Service (ToS) byte .
Setting CoS bits in the Layer 2 headers.
Setting EXP bits within the imposed or the topmost Multiprotocol
Label Switching (MPLS) label.
Setting qos-group, traffic-class, and discard-class bits.
Marker Action tab, specify the following:
Queueing Action: Queueing is used for traffic
congestion management. It entails the creation of queues, assignment of packets
to those queues based on the classification of the packet, and scheduling of
the packets in a queue for transmission.
Queueing Action tab, select the method by which traffic will be queued, either
Bandwidth or Priority, then specify the following:
Bandwidth—The amount of bandwidth to be assigned to the traffic
class, either in kilobits per second, or as a percentage of absolute guaranteed
bandwidth. If you selected to queue by bandwidth, you can also assign bandwidth
as a percentage of remaining bandwidth.
Limit— The maximum number of packets/bytes/milliseconds for all the individual
queues associated with this class. When the queue size exceeds this value,
packets will be dropped.
selected Bandwidth, specify the following:
Fair Queue—Check the check box to enable weighted fair queueing
Individual Queue Size—Relevant if fair queueing is enabled. Specify the maximum
number of packets allowed in each per-class queue during periods of congestion.
selected Priority, specify the following:
Burst Size (bytes)—The burst size configures the network to accommodate
temporary bursts of traffic. Range is 18 to 2000000 bytes. Default is 200
milliseconds of traffic at the configured bandwidth rate.
Priority Level—Classes under a policy map can have different
priority, from priority queue level 1 to 3. Packets on these queues are
subjected to less latency with respect to other queues. You cannot specify the
same priority level for two different classes in the same policy map.
Action: Traffic shaping regulates traffic by shaping it to a
Shaping Action tab, specify the following:
Average or Peak rate traffic shaping—Average rate shaping limits the
transmission rate to the CIR. Peak rate shaping configures the router to send
more traffic than the CIR. To determine the peak rate, the router uses the
following formula: peak rate = CIR(1 + Be / Bc) where Be is the Excess Burst
size and Bc is the Committed Burst size.
selected Peak rate traffic shaping, specify the burst size and the excess burst
size in bytes.
required, enable FECN Adaptive Shaping. Adaptive shaping estimates the
available bandwidth when backward explicit congestion notification (BECN)
signals are received. With FECN adaptive shaping, the router reflects forward
explicit congestion notification (FECN) signals as BECN signals.
FECN Adaptive Shaping is enabled, specify the Adaptive Rate, which is the
minimum bit rate to which the traffic is shaped.
RED Action: Weighted Random Early Detection (WRED)
is a congestion avoidance technique that implements a proactive queuing
strategy that controls congestion before a queue reaches its queue limit. WRED
combines the capabilities of the random early detection (RED) mechanism with IP
precedence, differential services code point (DSCP), and discard-class to
provide preferential handling of higher priority packets. When an interface
starts to become congested, WRED discards lower priority traffic with a higher
probability. WRED controls the average depth of Layer 3 queues.
In the RED
Action tab, specify the following:
Classification Mechanism—Select the basis upon which the WRED
drop policies are defined. For WRED, you define drop policies based on specific
packet classification, as follows:
CLP—Configures a drop policy for WRED based on a cell loss priority (CLP)
value. Valid values are 0 or 1.
CoS—Configures a drop policy for WRED based on the specified class of service
(CoS) bit associated with the packet. Valid values are from 0 to 7.
Class—Configures a drop policy for WRED based on a discard-class value. Valid
values are from 0 to 7. The discard-class value sets the per-hop behavior (PHB)
for dropping traffic. WRED based on discard-class is an egress function.
DSCP—Configures a drop policy for WRED based on a DSCP value. When configured,
the router randomly drops packets with the specified DSCP value, according to
the WRED thresholds you configure.
Precedence—Configures a drop policy for WRED based on an IP precedence level.
Valid values are from 0 to 7, where 0 typically represents low priority traffic
that can be aggressively managed (dropped) and 7 represents high priority
traffic. Traffic at a low precedence level typically has a higher drop
probability. When WRED drops packets, source hosts using TCP detect the drops
and slow the transmission of packets.
discard eligibility (DE) bit in the address field of a frame relay frame is
used to prioritize the discarding of frames in congested frame relay networks.
The frame relay DE bit has only one bit and therefore only has two settings, 0
or 1. If congestion occurs in a frame relay network, frames with the DE bit set
at 1 are discarded before frames with the DE bit set at 0.
Default—The default set of minimum thresholds, maximum thresholds, and Mark
Probability Denominator (MPD) settings for a class in the WRED profile.
required, enable ECN. ECN (Explicit Congestion Notification) marks packets
instead of dropping them when the average queue length exceeds a specific
threshold value. Routers and end hosts use this marking as a signal that the
network is congested and slow down packet transmission.
the thresholds and mark probability per valid value of the selected
classification mechanism. For example, if you are using Precedence, you can
define thresholds for each of the 7 valid values. The minimum threshold is the
minimum number of packets allowed in the queue. When the average queue length
reaches the minimum threshold, WRED randomly drops
some packets with the specified DSCP, IP precedence,
discard-class, or atm-clp value. Valid minimum threshold values are from 1 to
16,384. The maximum threshold is the maximum number of packets allowed in the
queue. When the average queue length exceeds the maximum threshold, WRED drops
all packets with the specified DSCP, IP precedence, discard-class, or atm-clp
value. Valid maximum threshold values are from the value of the minimum
threshold to 16,384.
Service Policy tab, you can configure Hierarchical QoS (H-QoS) which enables
you to specify QoS behavior at multiple levels of hierarchy. You can use H-QoS
to specify multiple policy maps to shape multiple queues together. All
hierarchical policy types consist of a top-level parent policy and one or more
child policies. The service-policy command is used to apply a policy to another
policy, and a policy to an interface.
configure H-QoS, navigate to the
Service Policy tab, select the
Enable check box, and use the
Service Policy drop-down menu to select the child
service policy. The selected child service policy will be associated to the
parent policy map that this action profile belongs to. Note that a child
service policy cannot act as a parent policy of the same policy map. For
example, if a child service policy called X belongs to a parent policy map Y,
then the child policy X cannot contain the service policy map Y.
Limitations: On Cisco IOS-XE devices such as Cisco ASR903, Cisco ASR907, Cisco
ASR920, and Cisco NCS42XX, the following H-QoS limitations are applicable: