Priority Traffic Dropping

[sometechguy]

We have the following QoS applied to a DS3 circuit out:

class-map match-all Voice

match ip dscp ef

!

!

policy-map WAN-EDGE

class Voice

priority percent 33

class class-default

fair-queue

random-detect dscp-based

policy-map shape

class class-default

shape average 1536000

service-policy WAN-EDGE

interface Serial0/0/0.1 point-to-point

bandwidth 1536

ip address x.x.x.x x.x.x.x

no ip redirects

frame-relay interface-dlci xxx

service-policy output shape

We are testing by generating voice and data traffic over the link using a packet generator (voice marked DSCP EF). When I run a "show policy-map interface serial0/0/0.1" during and after the test, it shows drops on the class-default and the voice class-map. Even when we send a very small amount of voice traffic it still shows drops in the DSCP EF queue. Shouldn't it only show drops on the class-default?

[paolo bevilacqua]

Hmm.. seems like you want a nested policy but it become peculiar because it ends having has two class-default.

Please configure a simple priority for serial interface. It doesn't need to be shaped and nested as you can configure FR native parameters for shaping as frame-relay commands.

(that is, you only need nesting under shaping for interfaces where you have no congestion or backpressure, e.g a fastethernet where you want to send only a certain amount of traffic).

Verify results with packet generator and latency/jitter analyzer if available, then you can experiment modifications for different values, drop strategies, etc.

hope this helps, please rate post if it does!