cat3750 QoS

[julxu]

Hi

I have a cat3570 configure QoS, but no special policy configed. I guess it is just default.

the related "show run all" information is:

mls qos map cos-dscp 0 8 16 24 32 46 46 56

mls qos rewrite ip dscp

mls qos

.....

interface GigabitEthernet1/0/1

description  as a wan link

no switchport

no ip arp inspection trust

ip arp inspection limit rate 15 burst interval 1

ip arp inspection limit rate 15

ip address ......

no iip redirects

no ip unreachables

no ip proxy-arp

no shutdown

speed nonegotiate

srr-queue bandwidth share 10 10 60 20

queue-set 2

priority-queue out

no mab

mls qos cos 0

mls qos trust dscp

mls qos dscp-mutation Default DSCP Mutation Map

snmp trap link-status

no mka policy

spanning-tree.......

question:

1. since I put queue-set 2 , so the egress is active? so, if voice packets go out, will keep the dscp code? or the packets with DSCP coded will not lose it?

2. the voice packets go out from the interface, there is no special policy, but by default, it is use QoS feature, WFQ?

3. the bandwidth allocation for the WFQ is 10 10 60 20?

4. by default, there is also a igress QoS existed?

Could anyone advice me what is the cat3750 QoS means, with the above configuration?

Specially, if the voice, video, conference traffic with DSCP marked come to this interface in/out, what will happen?

the purpose of digging this out is I want configure same QoS  on a router. is it possible?

Any comments will be appreciated

Thanks in advance

Julxu

[Joseph W. Doherty · Accepted solution]

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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.

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Posting

#1 queue-set 2 just allows for a different set of the of the queue parameters for your 4 egress queues

the 4 egress queues are enabled when qos is globally enabled

egress doesn't touch markings, ingress controls that

#2 by default, certain COS and/or DSCP markings are mapped to one of the 4 egress queues

also by default, when qos is enable, no markings are trusted on ingress, everything is remarked to zero, and all that traffic would go to the same egress queue

#3 3750s don't support WFQ, they do support SRR in shaped and/or share mode

in what you've posted, bandwidth sharing is PQ:10:60:20

#4 yes there is, to the fabric - it can be adjusted - only two queues - more limited features - seldom needs to be touched

To analyze QoS for a (or your) 3750, would need to see/know all the relevant QoS - you've only posted one interface and a couple of the global QoS statements

You might be able to somewhat mimic this 3750's QoS on a router, but as a router usually has much richer QoS features, I would suggest you take advantage of them.  For example, and for just some differences, the 3750 is configured with PQ and than with 3 queues running SRR share.  Routers PQ are PQ on all four of PQ's queues.  CBWFQ offers LLQ, but it's capped.  Something like:

policy-map Sample

class PQ

priority percent 99

class ten

bandwidth remaining 10

class sixty

bandwidth remaining 60

class twenty

bandwidth remaining 20

would come close to how the 3750 egress is configured but there's likely better QoS that could be done on the router.

[julxu]

Joseph

thanks a lot for previous helps.

Could you please adivce, what is igress setting, default setting?

also, another question:

- when voice/conference packets with dscp code travel to interface, it meets igress QoS, it take dscp code off, put it on  correct queue?

- and sent to output interface, the output interface remark the dscp code and sent it to correct queue according to dscp?

- so I can believe that the packets in/out of the switch will keep the dscp code even inside it take off/on process?

Please advice

Many Regards

julxu

[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

Could you please adivce, what is igress setting, default setting?

Sorry, don't know without researching or looking at a 3750 using the default.  As the ingress applies to congestion to the fabric, not normally something that need adjustment, especially with an -E or -X series.

- when voice/conference packets with dscp code travel to interface, it meets igress QoS, it take dscp code off, put it on  correct queue?
 - and sent to output interface, the output interface remark the dscp code and sent it to correct queue according to dscp?
 - so I can believe that the packets in/out of the switch will keep the dscp code even inside it take off/on process?

1st Q: Normally you don't remove ingress DSCP markings unless you remarking the packet.  The "final" ingress marking its what's used to select the egress queue.

2nd Q: I believe egress doesn't remark DSCP (on the 3750 series).

3rd Q: depends on config.  I think there's a way to preserve the original DSCP marking yet use a "temporary" for "internal" QoS processing.  Normally, though, you would either keep the original DSCP marking or remark before the packet leaves the box.  It would be unusual to preserve the original marking but want to treat the packet like it had another marking while in the 3750.