Auto QoS Discovery

Auto-Discovery


Started with the command:
(config-if)# auto discovery qos [trust]

Trust mode 


auto-discovery trusts the DSCP values in the IP header and uses it to classify packets, collect bandwidth statistics, calculate traffic average and traffic peak rate, then passes the data to the template module.

Untrust mode
auto-discovery uses NBAR to detect application on the network to collect data and perform statistical analysis.

To show the data that has been collected:
# show auto discovery qos [interface [interface type]]

QoS Tunnel

Where to configure Qos-preclassify for tunneling

You can apply a service policy to either the tunnel interface or to the underlying physical interface. The decision of where to apply the policy depends on the QoS objectives. It also depends on which header you need to use for classification.

• Apply the policy to the tunnel interface without qos-preclassify when you want to classify packets based on the pre-tunnel header.
  
  
• Apply the policy to the physical interface without qos-preclassify when you want to classify packets based on the post-tunnel header. In addition, apply the policy to the physical interface when you want to shape or police all traffic belonging to a tunnel, and the physical interface supports several tunnels.
  
  
• Apply the policy to a physical interface and enable qos-preclassify on a tunnel interface when you want to classify packets based on the pre-tunnel header.

Configuration of QoS tunnel

Router(config)# interface tunnel0
Router(config-if)# qos pre-classify

Voice Adaptive Traffic Shaping

Voice Adaptive Traffic Shaping is only acailable with MQC-based Frame-Relay traffic shaping, and only with LLQ enabled in sharper-queue. The goal of VATS is to throttle the PVC's sending rate once the system detected voice packets in the priority queue. The VATS feature is useful in the oversubscription scenaiio, where the customer sends traffic over the CIR. When the voice packet comes in the priority queue. the system will signal the shaper to slow its rate down to ensure router will never drop or delay any voice packets.

Command
policy-map class
shape fr-voice-adapt <deactivation N>
   where N = number of seconds to deactivate shaping after the last voice packet has been seen in the priority queue.

Referecence
CCIE R&S lab INE workbook I v5.0 

QoS Nest Configuration

Example of QoS nest 

Task: 

• Provider needs to limit the traffic from client not to exceed 1Gbps
• Voice is in 172.16.1.0/24 network
• Data is in 192.168.1.0/24 network
• Provider guaranteed Voice traffic to have minimum bandwidth of 20Mbps
• Use nest configuration and apply on R2 (Provider)

Configuration

Create Access-list for Voice traffic

ip access-list standard VOICE

 permit 172.16.1.0 0.0.0.255

!

Create Class for Voice traffic

class-map match-all VOICE

 match access-group name VOICE

!

Apply policy to guaranteed 20M for Voice traffic

policy-map VOICE-20M

 class VOICE

  bandwidth 20000

Nest QoS Configuration

policy-map INTERFACE-POLICY

 class class-default

  fair-queue

    police 20000000 conform-action transmit  exceed-action drop

  service-policy VOICE-20M

!

Apply Policy to interface

interface FastEthernet0/0

 ip address 10.10.10.2 255.255.255.0

 service-policy input INTERFACE-POLICY

 duplex auto

 speed auto

!

QoS

Quality Of Service (QoS)

In the network, there are different kind of traffic running back and forth across the link such as web traffic, voice, video and so on. In the case of congestion, if we treat every traffic as a same manner, it will impact the performance of some application especially real time application such as voice because voice is delay sensitive. In order to ensure performance of the application, QoS, therefore, comes into play.

In an IP packet, there is a 1-byte ToS field which refer to a type of service. ToS contains either IP precedence or DSCP value. These values differentiate traffic. For IP Precedence, there are 8 value (0-7) and DSCP (0-64).

We can assign either IP precedence or DSCP by using a policy-map according to the guide line below.

IP precedence

• 000 (0) - Routine
• 001 (1) - Priority
• 010 (2) - Immediate
• 011 (3) - Flash
• 100 (4) - Flash Override
• 101 (5) - Critical
• 110 (6) - Internetwork Control
• 111 (7) - Network Control

DSCP

Step to assign ToS to packet

• Identify traffic type : we may use access-list or prefix-list to accomplish this. 
• Match access-list by class-map statement.
• User Policy-map to assign type of service to the packet

Example


//Create Access-list
access-list 1 permit 172.16.1.0 0.0.0.255

access-list 101 permit ip 192.168.1.0 0.0.0.255 host 10.1.1.1

//Match access-list to class

!

class-map match-all network-172

 match access-group 1

class-map match-all network-192

 match access-group 101

!

// Apply policy-map to each class including class-default 

policy-map set-qos

 class network-192

  set ip precedence 5

 class network-172

  set ip dscp cs2

 class class-default

  set precedence 0