Bandwidth sharing between LLQ and CBWFQ classes

[santoshvijapur]

Dear All,

please help me to understand , bandwidth sharing between LLQ and CBWFQ .

I have configured QOS with LLQ .  one class is for strict priority and another class is bandwidth  , last is default

I have 3mbps link . 1 mbps bandwidth  I have configured strict priority . 1.5 mbps  bandwidth, 512kbps for default class

consider  strict priority class is totally empty , no traffic . and  Bandwidth and Default class are fully choked  ( 2mbps full) . is router allow to use strict priority class  ??? even though  it is completely nill usage . or it will not allow to use  Strict priority bandwidth 1 mbps class .

[Lei Tian]

Hi,

The queuing and scheduling might be little bit different on platform and code versions; in general, when there is no congestion on the link, any class of traffic can use all available bandwidth (unless there is policer for that class); during congestion, all class can use the guaranteed amount of bandwidth if needed, and they can share the rest available bandwidth base on their weight.

To your question, if the LLQ is empty other class can use the bandwidth assigned to LLQ.

Hope that answers your question.

HTH,

Lei Tian

[santoshvijapur]

Hi ,

when I configure the LLQ class and assign the bandwidth 1 mbps , as a strict priority . then policing will play a role . beow is configuration example .

In such scenario , is Strict priority class allow to pump traffic from   other class  , in its available free bandwidth

LLQ configuration exampls .  total link capacity is 4 mbps .

Class VOICE_VIDEO_CLASS
      Strict Priority
      Bandwidth 1024 (kbps) Burst 512000 (Bytes)  ---------------------------------------- 1 mbps ,no usage  , strict priority configured

    Class Hig-data-CLASS
      Bandwidth 2048 (kbps) Max Threshold 64 (packets) --------------------------------------  completely choked  , Bandwidth configured

    Class class-default
      Flow based Fair Queueing
      Bandwidth 0 (kbps) Max Threshold 64 (packets)  -----------------------   1mbps  completely choked ...

As what I understand , bandwidth class and default class traffic can allow to pump the traffic , but strict priority class  will not allow to pump traffic to other class and either  it will push its own traffic to other class . please suggest .

[Lei Tian]

The LLQ/CBWFQ mechanism does not engage unless there is back pressure due to congestion. Any traffic can use all available bandwidth.

When there is back pressure, the PQ is serviced before any of the other CBWFQs.To prevent the PQ from starving out the CBWFQs,  the PQ class of
traffic will be implicitly policed. So PQ cannot use other available bandwidth. If the PQ is empty, the bandwidth classes are allowed to use the bandwidth assigned to PQ based on their weight. There is no bandwidth reservation even it is called reserve bandwidth. Class-default is not subject to use available bandwidth if no 'bandwidth' configured on the class. Now that behavior has changed on HQF, because class-default has 1% bandwidth by default.

Please rate if it helps.

HTH,

Lei Tian

[santoshvijapur]

Thanks for the inputs . I have few more queries .

I have  below scanarios

I have configured    class name premium  where voice and multicast traffic is marked and bandwidth  reserved 10 mbps - precedence 5

Business class configure  20 mbps ( CBWFQ)   - precedence 4  , default class - precedence 0  30 mbps

from your inputs its got clear  if 10 mbps is fully utilized ( precedence 5)  it will not utilize    business class bandwidh ( CBWFQ )and default clas

2) Scanario  : If Business class is completely choked ( 20 mbps),  where i have configured   below configuration  .is it push the traffic   to default class and premium class if there is free bandwidth available.

  Class Business-Application-class
      set precedence 1

      bandwidth 20 mbps

3)  Scanario : if default class  30 mbps is completely choked , premium class and business class  nil utilized . is business class  pump the traffic to  premium class and business class .

4) Also I  need understand . If I am marking only traffic at CE  router and not allocating any bandwidth .  how  much by default  it will allocate bandwidth for each class . below are the configuration and   qos out put of each class .  please help.

7200-IOR#sh policy-map MPLS-QOS
  Policy Map MPLS-QOS
    Class voice-video-control-class
      set precedence 5
    Class Business-Application-class
      set precedence 1
    Class class-default
      set precedence 0

7200-IOR#sh class-map voice-video-control-class
Class Map match-all voice-video-control-class (id 2)
   Match access-group  150

7200-IOR#sh class-map Business-Application-class
Class Map match-all Business-Application-class (id 1)
   Match access-group  152

7200-IOR#sh class-map class-default
Class Map match-any class-default (id 0)
   Match any

7200-IOR#sh policy-map interface gigabitEthernet 0/1
GigabitEthernet0/1

  Service-policy input: MPLS-QOS

    Class-map: voice-video-control-class (match-all)
      690408597 packets, 66527045912 bytes
      5 minute offered rate 58000 bps, drop rate 0 bps
      Match: access-group 150
      QoS Set
        precedence 5
          Packets marked 690408624

    Class-map: Business-Application-class (match-all)
      561255 packets, 70341513 bytes
      5 minute offered rate 1000 bps, drop rate 0 bps
      Match: access-group 152
      QoS Set
        precedence 1
          Packets marked 561255

    Class-map: class-default (match-any)
      3801832539 packets, 1396390966707 bytes
      5 minute offered rate 4024000 bps, drop rate 0 bps
      Match: any
      QoS Set
        precedence 0
          Packets marked 3801832565

[Lei Tian · Accepted solution]

Hi,

1),yes

2),yes

3),I guess you mean default class use business and premium class. The answer is yes.

4),For software based router, the default queueing is FIFO for GE interface. All classes share the link bandwidth.

HTH,

Lei Tian

[santoshvijapur]

Hi Thanks for the input ,

I need more help from you    .    I have 6509 core switch . where CEF is ruunning .  I am applying  QOS for  the one of the application

where  I am calling ACL  and defining    1) perimit ip host 10.200.250.10 any

                                                          2) permit udp range 49000 49100 any     

In clas-map OCS  for the ACL i am marking ip  precedence  5 .  and applying  on the interface

for the second statement of ACL  i am finding  hits  , same time for the first statement ACL  I am not finding ACL hits .  As CEF being eanbled  is that reason i am not finding hits at ACL at first statement  and not marking the packets for precedence 5 . is there any way to check precedence 5 has been marked for the packetes . please suggest .

On the second scenario .  for the above configuration .   I am applying  "service-policy output  LLQ"  on two interface  .( both interface are connecting to my WAN router )  when I try to apply  i got below error , is it makes any issue.please help .

6509-DC-Core(config)#int gigabitEthernet 5/2

6509-DC-Core(config-if)#service-policy output LLQ
QoS: Match criteria in class OCS on GigabitEthernet5/2 cannot simultaneously have match dscp | precedence | exp and match ACL
QoS: Match criteria in class OCS on GigabitEthernet5/2 cannot simultaneously have match dscp | precedence | exp and match ACL

6509-DC-Core(config)#int gigabitEthernet 3/6

6509-DC-Core(config-if)#service-policy output LLQ
QoS: Match criteria in class OCS on GigabitEthernet5/2 cannot simultaneously have match dscp | precedence | exp and match ACL
QoS: Match criteria in class OCS on GigabitEthernet5/2 cannot simultaneously have match dscp | precedence | exp and match ACL