Egress Queueing on Cisco 6504-E and Cisco 6509-E Line cards

[mohankumarm]

Hello,

In our network environment,  we have the following configuration:

Cisco 6509-E(Sup-2T) as the Core switch equipped with line card module WS-X6848-SFP (1 GE)

Cisco 6504-E (VSS-720-10G Sup) as the distribution service layer switch equipped with line card module WS-X6704-10GE

.

Both the line card modules terminate Layer 3 connections from the access/core layer.

The QoS trust state is "DSCP" on the line card interfaces and on the 6504-E "mls qos trust dscp" is explicitly configured to trust DSCP values.           As can be seen from the switch interface capability outputs below, the "QoS queueuing mode" on both the line cards is "CoS" only, and DSCP egress queueing is not available in the "wrr-queue" interface configurations. Similar issue exists on port channel member interfaces on the core switch Sup-2T as well.

CORE01#sh int gig2/1 cap

GigabitEthernet2/1

  Model:                 WS-X6848-SFP

  Type:                  1000BaseSX

  QOS scheduling:        rx-(2q8t), tx-(1p3q8t)

  QOS queueing mode:     rx-(cos), tx-(cos)

VSS01#sh  int t1/2/1 cap  

TenGigabitEthernet1/2/1

  Model:                 WS-X6704-10GE

  Type:                  10Gbase-LR

  QOS scheduling:        rx-(8q8t), tx-(1p7q8t)

QOS queueing mode:     rx-(cos), tx-(cos)

CORE01(config-if)#wrr-queue ?

  bandwidth      Configure WRR minimum bandwidth with weights or percentages

  cos-map        Configure cos-map for a queue threshold ------------------------------------------> Cos  Map only No DSCP

  queue-limit    Configure queue-limit

  random-detect  Configure random-detect

  shape          Configure SRR maximum queue bandwidth with weights or

                 percentages

  threshold      Configure queue tail-drop thresholds

VSS01(config-if)#wrr-queue ?

  bandwidth      Configure WRR minimum bandwidth with weights or percentages

  cos-map        Configure cos-map for a queue threshold  ------------------------------------------> Cos  Map only No DSCP

  queue-limit    Configure queue-limit

  random-detect  Configure random-detect

  threshold      Configure queue tail-drop thresholds

In the above scenario, how should Egress Queueing be implemented and what are the best practises ? If "wrr-queue" is not supported for DSCP, is it recommended to configure "Policy Map" for Egress queueing and/or any other related queueing configurations and then apply the Egress service policy outbound on the interface. Also, if egress queueing policy map config is used, can this be used for all the other DSCP/COS line cards in the system, so that the configuration is consistent on the 6500 network.

Thanks and Regards,

Mohan

:

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

On the 6500s, line cards that only support internal CoS prioritization you can map DSCP into different internal CoS values.  There's a default mapping, but you can selectively override, e.g. "mls qos map dscp-cos 40 41 42 43 44 45 47 to 4".

See: http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND_40/QoSCampus_40.html#wp1107330

[mohankumarm]

Hi Joseph,

Thank you for your response and also for the links to the SRND. I am aware of the internal mapping table, so in this case, do you still apply the "wrr-queue cos-map .." egress queueing commands on the interface, which should take effect once the dscp to cos translation is in place..I am a bit confused here as i thought the mapping tables will take effect only after the packets enters the switch(ingress) and not before, so was thinking along the lines of PFC QoS.

Thanks and Regards,

Mohan

[Joseph W. Doherty · Accepted solution]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

My understanding is you use wrr-queue cos-map as you would for the CoS values understanding DSCP values have been mapped into those CoS values.

If you look at figure 2-25, in the reference I provided, you'll see "Final internal DSCP is mapped to CoS" and ""DSCP -> CoS rewrite" when dealing with the egress port QoS.

[mohankumarm]

Hi Joseph,

Thanks very much indeed and yes it is very clear explanation now and we are now applying "wrr-queue cos-map" or if supported "wrr-queue dscp-map" interface commands consistently on the various line cards on the Cat65K and we are using MQC for marking if required and no MQC is used for egress queueing.

Thanks again.

Best Regards,

Mohan