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In the Architecture part of Cisco CCNP ENCOR v1.2 lessons, there is a QoS lesson named “Interpret QoS configurations”. Here, we will focus on Quality of Service and How to Interpret QoS Configurations on Cisco devices. We will see a QoS Configuration and then you will learn the meaning of various of Cisco QoS Commands.
In the first Interpret QoS Configuration example we will focus on voice, video and default traffics. We will see a Cisco QoS Configuration on Packet Tracer and then we will interpret what is the meaning of this Quality-of-Service Configuration. Our configuration is below:
class-map match-any VOICE
match dscp ef
class-map match-any VIDEO
match dscp af41
policy-map WAN-QOS
class VOICE
priority percent 20
class VIDEO
bandwidth percent 30
class class-default
fair-queue
interface GigabitEthernet0/0
service-policy output WAN-QOS
Firstly, let’s explain the basic points of this Quality-of-Service Configuration. The first two parts are classification in this configuration.
Here, DSCP EF traffic is classified as VOICE and DSCP AF41 traffic is classified as VIDEO.
Voice traffic uses LLQ, because of the priority command.
Video traffic gets a minimum bandwidth guarantee of 30%.
Default traffic uses fair-queue.
And lastly, this policy is applied outbound direction on GigabitEthernet0/0.
Voice traffic gets the lowest latency.
The command “priority percent 20” creates the priority queue.
The policy is applied on GigabitEthernet0/0 of the device.
The policy is applied outbound direction.
DSCP AF41 traffic matches the VIDEO class and it gets 30% minimum bandwidth.
In the second Interpret QoS Configuration example, we will focus on QoS Policing. We will use Access-List to match policies with the desired traffic.
access-list 101 permit ip 10.10.10.0 0.0.0.255 any
class-map BULK-DATA
match access-group 101
policy-map INTERNET-POLICY
class BULK-DATA
police 50000000
conform-action transmit
exceed-action drop
class class-default
bandwidth percent 20
interface GigabitEthernet0/1
service-policy output INTERNET-POLICY
In this QoS Policing configuration, the traffic from 10.10.10.0/24 matches the BULK-DATA class with an access list and “class-map” command.
This BULK-DATA is limited to 50 Mbps. This means that the traffic above 50 Mbps will be dropped. This is basically policing not shaping. It drops the traffic instead of queuing.
In this policy configuration, Class-default receives a minimum 20% bandwidth guarantee.
Traffic from 10.10.10.0/24 matches the BULK-DATA class.
The command “police 50000000” under policy-map INTERNET-POLICY and under class BULK-DATA limits traffic to 50 Mbps.
This is policing so the traffic above 50 Mbps is dropped.
This is a QoS policing example.
In this QoS configuration, class-default receives 20% minimum bandwidth.
In the third Interpret QoS Configuration example, we will focus on QoS Marking and Shaping. You will learn how marking and shaping commands means on a Quality-of-Service configuration on a Cisco router. Our packet tracer configuration example is below:
class-map match-any BUSINESS-APP
match protocol http
match protocol https
policy-map MARK-BUSINESS
class BUSINESS-APP
set dscp af31
class class-default
set dscp default
interface GigabitEthernet0/2
service-policy input MARK-BUSINESS
policy-map WAN-SHAPER
class class-default
shape average 100000000
interface GigabitEthernet0/3
service-policy output WAN-SHAPER
In the first lines of this configuration, HTTP and HTTPS traffic are classified as BUSINESS-APP. And this BUSINESS-APP traffic is marked with DSCP AF31 in the second configuration part.
The remaining traffic is marked as default.
In this Marking and Shaping configuration, marking is applied inbound on GigabitEthernet0/2 and shaping is applied outbound on GigabitEthernet0/3.
Traffic is shaped to an average rate of 100,000,000 bps (100 Mbps). This means that, when the traffic exceeds 100 Mbps:
HTTP and HTTPS traffic match BUSINESS-APP.
BUSINESS-APP is marked with DSCP AF31.
Marking is applied on GigabitEthernet0/2.
Shaping is applied on GigabitEthernet0/3.
Policing drops excess traffic, while shaping queues excess traffic and sends it later.
Policing drops or remarks traffic that exceeds a configured rate. Shaping buffers excess traffic and sends it later, creating a smoother traffic flow.
Look for the priority command inside a policy-map. This indicates LLQ.
Example:
class VOICE
priority percent 20
Look for the bandwidth command. This indicates CBWFQ.
Example:
class VIDEO
bandwidth percent 30
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