enabled. The show auto qos
interface command can also be used with Frame Relay DLCIs
and ATM PVCs. Step 3 Display the data
collected during the Auto Discovery phase: - To display
the packet statistics of all classes that are configured for
all service policies either on the specified interface or
subinterface or on a specific PVC on the interface, use the
show policy-map interface command as shown in Figure
.
- The counters displayed after you enter the show
policy-map interface command are updated only if there is
congestion on the interface. The command will also display
policy information about Frame Relay PVCs, but only if Frame
Relay traffic shaping (FRTS) is also enabled on the interface
(manually or by Cisco AutoQoS).
Monitoring Cisco
AutoQoS on Switches
Follow these three steps to monitor
Cisco AutoQoS on Cisco Catalyst switches: Step 1
Examine Cisco AutoQoS templates and initial configuration:
- Use the show auto qos command to display the
initial Cisco AutoQoS VoIP configuration on the switch. Figure
shows the command syntax and an example. To display any user
changes to that configuration, use the show
running-config command. The show auto qos and the
show running-config command output can be compared to
identify the additional user-defined QoS settings. From the
show command output, you can see that the switch has
four output WRR queues available with weights 20, 1, 80 and 0
for queues 1, 2, 3, and 4 respectively. The wrr-queue
cos command shows the CoS mapping for each queue as follows
(the first number is the queue ID, the second one is the
threshold id, the other numbers are CoS values).
-
Queue 4 is used for high-priority traffic (a value of 0 within
the wrr-queue bandwidth command and a mapping of CoS 5
to queue 4 using the wrr-queue cos-map command).
- Queue 2 is not used at all (a value of 1 within the
wrr-queue bandwidth command and no mapping of CoS to
queue 2 using the wrr-queue cos-map command).
-
Queue 1 gets 20 percent of any bandwidth not being used by
Queue 4 and provides CoS 0, 1, 2, and 4.
- Queue 3 gets
80 percent of any bandwidth not being used by Queue 4 and
provides CoS 3, 6, and 7.
- The CoS to DSCP mapping is
shown, as is the trusted IP phone connection.
Step 2 Explore interface-level autogenerated QoS
parameters: - Use the show mls qos interface
command as shown in Figure to display QoS information on the
Cisco Catalyst switch at the interface level, including the
configuration of the egress queues and the CoS-to-egress-queue
maps, the interfaces that have configured policers, and ingress
and egress statistics (including the number of bytes
dropped).
- If no keyword is specified with the show
mls qos interface command, the port QoS mode (DSCP trusted,
CoS trusted, untrusted, and so forth), default CoS value,
DSCP-to-DSCP-mutation map (if any) that is attached to the
port, and policy map (if any) that is attached to the interface
are displayed. If a particular interface is not specified, the
information for all interfaces is displayed.
Step 3 Examine CoS-to-DSCP maps: - Use the show
mls qos maps command, as shown in Figure to display the
current DSCP and CoS mappings. All the maps are globally
defined.
- The cos-dscp keyword presents the
default CoS-to-DSCP map. The supported CoS values are
0–7.
- The dscp-cos keyword presents the default
DSCP-to-CoS mapping. The supported DSCP values are 0, 8, 10,
16, 18, 24, 26, 32, 34, 40, 46, 48, and 56.
- After a
default map is applied, you can define the CoS-to-DSCP or
DSCP-to-CoS map by entering consecutive mls qos map
commands.
Content
5.2 Mitigating Common Cisco AutoQoS
Issues 5.2.1 Automation with Cisco AutoQoS
Figure lists key QoS requirements of typical enterprises. Cisco
AutoQoS automates QoS deployment for the most common enterprise
scenarios and enables several Cisco IOS QoS mechanisms to meet
the QoS requirements of various applications and traffic types
discovered in the enterprise network. Enterprise requirements
include the following: - Identify trust boundary and
extended trust boundary and protocols of interest.
-
Determine the number of differentiated services (DiffServ)
classes that will be defined for the enterprise network.
- Re-mark traffic based on local policy requirements.
- Determine the queuing methods that should be
enabled.
- Define the individual class bandwidth needed
to fulfill real-time traffic requirements and provide minimum
bandwidth guarantees for other applications.
- Define
transport-specific QoS features (traffic shaping, Multilink PPP
[MLP], and transmit ring [tx-ring] settings).
- For
low-bandwidth links (less than 768 kbps), specify necessary QoS
features (compressed Real-Time Transport Protocol [cRTP], MLP
link fragmentation and interleaving [LFI], or Frame Relay
Fragmentation [FRF.12]).
- Define the alarm and event
settings for monitoring purposes.
In addition, in a
LAN environment, Cisco AutoQoS also has these requirements:
- Determine class of service (CoS)-to-differentiated
services code point (DSCP) and IP precedence-to-DSCP
mappings.
- Map CoS values to different egress queues
(via CoS-to-DSCP maps).
- Set the queue sizes and
weighted round robin (WRR) weights (that is, the appropriate
WRR settings for Fast Ethernet interfaces versus Gigabit
Ethernet interfaces).
Content
5.2 Mitigating Common Cisco AutoQoS
Issues 5.2.2 DiffServ QoS Mechanisms Enabled
by Cisco AutoQoS Using Cisco best-practices
recommendations, Cisco AutoQoS enables several QoS mechanisms
to ensure optimal performance of autodiscovered enterprise
applications. Cisco AutoQoS automatically provisions six QoS
mechanisms using DiffServ technology as shown in Figure and
described in detail below. Classification
Packet
classification provides the ability to partition network
traffic into multiple priority levels or classes of service.
For example, by using the Internet Engineering Task Force
(IETF)-defined DSCP values specified in DiffServ standards RFC
2474 and 2475, networks can categorize application traffic into
a maximum of 64 traffic classes. Cisco AutoQoS defines up to 10
classes. When packets are classified, use the various QoS
features in Cisco IOS software to assign the appropriate
traffic-handling policies for each traffic class. Cisco AutoQoS
either reuses the classification based on DSCP or IP precedence
and CoS from the adjacent device (for example, the router or
switch closer to the network edge) in trusted mode or activates
Cisco Network-Based Application Recognition (NBAR) to classify
the traffic on an ingress interface in untrusted mode. In
either case, Cisco AutoQoS defines classes using the Cisco
Modular QoS CLI (MQC) class maps. Marking
Marking
tools mark a packet or flow with a specific priority. This
marking is performed at a trust boundary. Classification and
marking should take place at the network edge, typically in the
wiring closet switches, within the Cisco IP phones themselves,
or at voice endpoints. Packets can be marked as important by
using Layer 2 CoS settings in the user priority bits of the
802.1p portion of the 802.1Q header or the IP precedence or
DSCP bits in the type of service (ToS) byte of the IP version 4
(IPv4) header. For example, all Cisco IP phone Real-Time
Transport Protocol (RTP) packets should be tagged with either
of these values: - CoS value of 5 for the Layer 2
802.1p settings and a DSCP value of expedited forwarding
(EF)
- IP precedence value of 5
- Additionally,
all control packets should be tagged with a Layer 2 CoS value
of 3 and a Layer 3 DSCP value of 24–31 (or IP precedence value