QOS Interface Policy Output Default DSCP code

[tsalt]

I have QOS configured on a router and when I do "show policy interface serial 0/0:0"

I see packets under the default section of the DSCP column. I have enclosed an example.

Can anyone explain what this column section is for, and why if I should see entries in this value.

[Andrew Chan]

If I understand correctly, the traffic match to the class test and not mark with a specific dscp value will fall into the default (dscp 0). The the policing is going to mark the packet with dscp value to 26, 28 or 30 depends on whether the rate of the traffic. You should see the dscp value changed on your next hop router.

[tsalt]

Thanks for the reply.

All traffic should be marked as below:-

policy-map test

class test

bandwidth 8000

random-detect dscp-based

random-detect dscp 26 683 2049 1

random-detect dscp 28 410 1366 1

random-detect dscp 30 205 683 1

police 8000000 1000000 1500000 conform-action set-dscp-transmit 26 exceed-action set-dscp-transmit 28 violate-action set-dscp-transmit 30

which was why I was querying traffic entering the default queue.

[Andrew Chan]

Cisco IOS classifies traffic before policing and shaping. When the packet arrived with dscp 0 will be classified in the default queue and pass to the policer for action, either delivery or drop. The packets marked during the delivery will not put back into the queue to be re-classified. That's why all traffic is shown received in default queue.

[mheusinger]

Hi,

obviously you apply your service-policy on output. What does your class-map look like, what do you try to match? Are you sure you do not catch locally generated packets from the router? can you pllease post the complete "show policy-map interface"?

What looks strange is, that you get only 18 packets at all. Can you create more load and f.e. ping through the router and check the result again?

The order of QoS operation on output should be

1) classify

2) mark

3) police

4) shape

5) WRED

6) queue

7) LFI

I agree that your policer should at least mark conforming traffic.

What could also interfere with your expected behaviour is, that packets CEF switched will not show up in the policy-map queueing section. So make sure you overload your interface to get packets in the L3 queueing system.

Regards, Martin

[tsalt]

Dear Martin,

Thanks for your assistance. Enclosed is the configuration for the class. I have changed the name as this is from a working customer router. There are other classes configured in the ploicy, and the last one has an ACL that catches all IP Packets.

I am confused about your sentence which states that "CEF switched packets not showing in the queueing section". Because if I clear the counters, and watch the policy I can see the AF26 counters increasing with the packets being marked by the interface, and only a small load on teh link. I beliveve for QOS to work we need CEF configured.