QoS Statistics on the various Catalyst platforms

andrew.butterworth · ‎10-08-2005

I have been testing QoS on the various Catalyst platforms recently (2950, 3550, 3560/3750) and am a bit disappointed with the statistics that are available from the CLI. The 3550 seems to offer the best with the 'mls qos monitor' interface command.

On all platforms none report any statistics for the the input policy-maps - i.e. 'show policy-map interface fastethernet0/1'.

The 2950 is particulary bad (EMI versions) as there is no indication anywhere that shows if the policy has done anything (I have been using Ethereal to look at egress traffic to see the DSCP re-classification).

Are there any tools available that will allow me to interogate QoS statistics on these platforms?

Thanks

Andy

szahid · ‎10-08-2005

Andy -

I agree with you. 2950 ( and 2940 ) do not have any statistics that can help you with qos verification at all specially in the case of DSCP marking. All you have to do is use the sniffer to see if the dscp has been re-written.

If you are doing policing , what you can do is just check the counters on the egress port to see if the policer is taking effect.

Without the policer:

2950# show interface counters

Port InOctets InUcastPkts InMcastPkts InBcastPkts

Fa0/4 1320000 20000 0 0

Port OutOctets OutUcastPkts OutMcastPkts OutBcastPkts

Fa0/1 1321992 20002 21 0

With the Policer:

2950# show interface counters

Port InOctets InUcastPkts InMcastPkts InBcastPkts

Fa0/4 1320000 20000 0 0

Port OutOctets OutUcastPkts OutMcastPkts OutBcastPkts

Fa0/1 50798 743 27

In the above case , I applied the policer on Fa0/4 for traffic going out of Fa0/1 . See how the counters are changing after applying the policer. Thats just about the only tool you can use to verify the policer. As I had said earlier , no command to check the dscp values.Also an important thing to note is the number of packets allowed by the policer to get through to Fa0/1 may be higher then expected since the policing rate used by the switch does not include the 8 bytes of preamble and 12 bytes of Inter Frame Gap (IFG) associated with each Ethernet frame. Depending on the frame size of the Ethernet traffic (the preamble and IFG with be more noticeable on smaller sized frames), the policing rate may seem incorrect, but in reality, it is working correctly. The burst value in the policer will also effect the policed rate.

Platforms like 3750 manager per dscp statistics with command sh mls qos interface statistics. In 3750/3560/2970 , there is no need to do mls qos monitor command , the switch automatically keeps track of per dscp statistics for 64 unique dscp values. 3550 can keep statistics for only upto 8 dscp values.

Hope this helps.

Salman Z.

andrew.butterworth · ‎10-09-2005

Hi Salman and thanks for the reply.

With the 3550 the 'show mls qos statistics' shows the received DSCP value and the re-classified DSCP value (as long as monitoring is enabled). There isn't an equivilent on the 3560/3750 platform that I can see; the show mls qos statistics command doesn't have the same output?

Andy

szahid · ‎10-09-2005

Andy -

It does not have the same o/p , but it has even better o/p. As it gives you the ingress statistics for all 64 dscp values as well as egress dscp statistics for all 64 dscp. For example , a packet comes in with dscp of 10 on Fa0/1 and you rewrite it to dscp of 46 as it levaes fa0/2. You will observe the dscp of 10 coming in on Fa0/1 in the ingress part of the o/p and you will see dscp of 46 on Fa0/2 in egress part of the o/p. Basically the bottom line is you have to take the command o/p on the egress port for checking the reclassified dscp on a 3750. On 3550 , the ingress port maintains that value.

HTH.

Salman Z.

andrew.butterworth · ‎11-24-2005

Salman

I am not conviced the 3750 output IS better than the 3550. When you only have 2 active ports - ingress and egress I agree the stats are easy to read. If you have many active ingress ports the egress (uplink) stats are impossible to fully understand. The 3550's 'Classified' 'Policed' & 'Dropped' columns in the 'show mls qos interface statistics' are good as it tells you on a per-interface basis how much is being policed.

Are there any management tools available that can interogate the switches for this (and possibly more extensive) QoS statistics?

Thanks

Andy

eringaard · ‎10-11-2005

What about cat 4500 w/Supervisor III and higher or 6500s? anyone know how to check packet cos/dscp-queue mappings on those? I can show my settings with show qos maps dscp tx-queues, but it doesn't show switch operation. I just can't really tell whats happening.