WRED and DSCP configuration

[yuan]

I have this question regarding the following QoS configuration on a policing router (assuming dscp marking has already been done by a different router),

class-map match-any video

match ip dscp af41

match ip dscp af42

policy-map qos

class video

bandwidth 20

random-detect dscp-based

interface serial0/0

service-policy qos

my question is, does this configuration mean although packets that are marked "af41" and "af31" are sharing the same bandwidth of 20%, when congestion happens, packets marked with af42 will have a higher probability of being dropped than af41?

[dgahm · Accepted solution]

Yes, the defaults for AF41 would mean that when there are between 32 and 40 AF41 packets queued, 1 out of 10 would be discarded. Over 40 they all would be discarded. For AF42 the minimum threshold is 28 with the max 40, and the same probability of 1/10.

You can change this:

random-detect dscp AF42 10 30 5

This would discard 1 out of 5 packets when the queue depth is between 10 and 30.