Cisco QoS features like LLQ and CBWFQ let us to prioritize and guarantee delay and bandwidth for defined class of traffic.
CBWFQ configuration allows to configure the BW requirements for specific class of service. First we have to defined the class and match the specific type of traffic, then assign BW limit in the policy that will be reserverd during interface congestion. Standard bandwidth command with BW in Kbps under class can be used for above. The drawback of this type of configuration is need to adjust the BW speed definition each time once we have changed the access speed.

IOS allows to tune the QoS configuration to define kind of QoS template that will use BW class ratio accross function similar devices without need for reconfiguration of BW parameters each time when access speed change. LLQ defines the priority queue for the delay sensetive traffic. Additionaly for business critical traffic CBWFQ needs to be configured. We have two options to confgure the QoS template: bandwidth percent and bandwidth remaining percent per class options.

I have defined 4 classes that will be used to presents configuration options.
class-map match-all TELNET
 match protocol telnet
class-map match-all HTTP
 match protocol http
class-map match-all SMTP
 match protocol smtp
class-map match-all VoIP
 match protocol rtp

Option 1 – bandwidth percent
First option to define BW template is to use bandwidth percent command instead of just bandwidth under class in policy map configuration. BW will be calculated based on the interface’s BW, so in case Fast Ethernet it will be 100Mbps. Priority percent 10 for PQ or bandwidth percent 10 in CBWFQ it’s 10% of 100Mbps.

By default, available interface BW is defined based on the physical port speed unless you configure the bandwidth command under interface to set access speed to something less (SLA access). Additionaly Cisco IOS has Default Class (class-default) with reserved the 25% of interface BW that match all undefined traffic (you can change it with max-reserved-bandwidth command under interface mode).

Let’s configure the first policy based on option 1:
R1(config)#policy-map LLQ
R1(config-pmap)#class VoIP
R1(config-pmap-c)#priority percent 10
R1(config-pmap-c)#class HTTP
R1(config-pmap-c)#bandwidth percent 10
R1(config-pmap-c)#class SMTP
R1(config-pmap-c)#bandwidth percent 50
R1(config-pmap-c)#class TELNET
R1(config-pmap-c)#bandwidth percent 30

The first way choice is to configure the bandwidth percent to fil 100% of interface speed, but due to class-default the available BW to share is 75%. In the above example we have defined 4 classed and assigned 100% of interface BW, here let’s try to assign the LLQ policy to the inerface:
R1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#int fa0/0
R1(config-if)#service-policy output LLQ
I/f FastEthernet0/0 class TELNET requested bandwidth 30%, available only 5%
R1(config-if)#

We can observe the error message that is saying that we have just 5% of available BW, this is due to 25% reserved for default class. OK so let change reserved BW for TELNET to 5%, assign policy to the interface and see the policy.
R1#show policy-map interface fastEthernet 0/0
 FastEthernet0/0
  Service-policy output: LLQ
    Class-map: VoIP (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol rtp
      Queueing
        Strict Priority
        Output Queue: Conversation 264
        Bandwidth 10 (%)
        Bandwidth 10000 (kbps) Burst 250000 (Bytes)
        (pkts matched/bytes matched) 0/0
        (total drops/bytes drops) 0/0
    Class-map: HTTP (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol http
      Queueing
        Output Queue: Conversation 265
        Bandwidth 10 (%)
        Bandwidth 10000 (kbps)Max Threshold 64 (packets)
        (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0
    Class-map: SMTP (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol smtp
      Queueing
        Output Queue: Conversation 266
        Bandwidth 50 (%)
        Bandwidth 50000 (kbps)Max Threshold 64 (packets)
        (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0
    Class-map: TELNET (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol telnet
      Queueing
        Output Queue: Conversation 267
        Bandwidth 5 (%)
        Bandwidth 5000 (kbps)Max Threshold 64 (packets)
        (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0
    Class-map: class-default (match-any)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: any

Policy has been defined for Fast Ethernet so LLQ and CBWFQ have 75Mbps traffic reserved, below BW calculation details:

VoIP = 100Mbps * 0,1 = 10Mbps
HTTP = 100Mbps * 0,1 = 10Mbps
SMTP = 100Mbps * 0,5 = 50Mbps
TELNET = 100Mbps * 0,05 = 5Mbps

Option 2 – bandwidth remaining percent
Second option to define BW is to use bandwidth remaining percent command. The idea of this type of configuration is to first reserve the BW for the PQ thru priority percent command and next divides the available remaining BW between defined classes.
Let’s configure below:
R1(config)#policy-map LLQ
R1(config-pmap)#class VoIP
R1(config-pmap-c)#priority percent 10
R1(config-pmap-c)#class HTTP
R1(config-pmap-c)#bandwidth remaining percent 10
R1(config-pmap-c)#class SMTP
R1(config-pmap-c)#bandwidth remaining percent 50
R1(config-pmap-c)#class TELNET
R1(config-pmap-c)#bandwidth remaining percent 40
R1(config-pmap-c)#int fa0/0
R1(config-if)#service-policy output LLQ

For class VoIP priority percent 10 will be equal 100Mbps*0,1=10Mbps, BW Remaining is = (100-10)Mbps * 0,75= 67,5Mbps. So BW Remaining will be used as reference for all classes.
For class HTTP bandwidth remaining percent 10 will be equal BW Remaining*0,1 = 67,5Mbps*0,1= 6,75 Mbps.
For class SMTP bandwidth remaining percent 50 will be equal BW Remaining*0,5 = 33,75 Mbps.
For class TELNET bandwidth remaining percent 40 will be equal BW Remaining*0,4 = 27 Mbps.
By default Burst for Strict Priority queue is equal 20% of the PQ’s BW so 20% of 10Mbps, (10000000bitów/8)*0,2=250000B

R1#show policy-map interface fa0/0
 FastEthernet0/0
  Service-policy output: LLQ
    Class-map: VoIP (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol rtp
      Queueing
        Strict Priority
        Output Queue: Conversation 264
        Bandwidth 10 (%)
        Bandwidth 10000 (kbps) Burst 250000 (Bytes)
        (pkts matched/bytes matched) 0/0
        (total drops/bytes drops) 0/0
    Class-map: HTTP (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol http
      Queueing
        Output Queue: Conversation 265
        Bandwidth remaining 10 (%)Max Threshold 64 (packets)
        (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0
    Class-map: SMTP (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol smtp
      Queueing
        Output Queue: Conversation 266
        Bandwidth remaining 50 (%)Max Threshold 64 (packets)
        (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0
   Class-map: TELNET (match-all)
      0 packets, 0 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: protocol telnet
      Queueing
        Output Queue: Conversation 267
        Bandwidth remaining 40 (%)Max Threshold 64 (packets)
        (pkts matched/bytes matched) 0/0
        (depth/total drops/no-buffer drops) 0/0/0
   Class-map: class-default (match-any)
      30 packets, 2851 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: any

Above examples are Cisco recommended ways to deploye CE QoS configuration for different access speed port.

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