PFC and software qos

Unanswered Question
Aug 18th, 2010

Hi, recently I enabled MLS qos i understand this works with packets that are hardware switched in the PFC. Is it recomend or should i also setup some other queueing method such as CBWFQ for packets that get software switched?


Mod Ports Card Type                              Model              Serial No.
--- ----- -------------------------------------- ------------------ -----------
  1   48  SFM-capable 48-port 10/100 Mbps RJ45   WS-X6548-RJ-45     SAL0751QS8S
  2   48  SFM-capable 48-port 10/100 Mbps RJ45   WS-X6548-RJ-45     SAL0749Q6TF
  5    2  Supervisor Engine 720 (Active)         WS-SUP720-3BXL     SAL09158YJ2
  6    2  Supervisor Engine 720 (Hot)            WS-SUP720-3BXL     SAL1028UPGH


  8    0  2 port adapter FlexWAN                 WS-X6182-2PA       SAD04320GGC



core.#sh mls qos
  QoS is enabled globally
  Policy marking depends on port_trust
  QoS ip packet dscp rewrite enabled globally
  Input mode for GRE Tunnel is Pipe mode
  Input mode for MPLS is Pipe mode
QoS Trust state is DSCP on the following interface
Fa1/14 Fa1/15 Fa1/17 Fa1/47 Fa2/27
  Vlan or Portchannel(Multi-Earl) policies supported: Yes
  Egress policies supported: Yes

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kyukim Wed, 08/18/2010 - 12:35

Hi,



Either packet is switched in HW or not is not relevant to QoS policy because QoS policies will be applied before pkt is forwarded to CPU or forwarded in HW.

It is more important that packet is coming to which interface on which module, like SIP or FLEXWAN or LAN Switching module as they have different HW structure and support QoS differently.


If you have only SIP modules with SPAR cards or FLEXWAN cards, then you can use MQC. 


http://cisco.biz/en/US/docs/interfaces_modules/shared_port_adapters/configuration/6500series/76cfgsip.html#wp1177665


With LAN switching modules, CBWFQ/LLQ/CAR/GTS/NBAR are not supported in HW on PFC/DFCand will be processed in SW.

So, it might cause high CPU.


For PFC QoS, enabling mls qos is not enough.

You can read below config guide for more PFC QoS configuration.

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/guide/qos.html


KK.

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