table-map and class match - processing

[hurgazoid]

hi all,

trying to get through a existing QoS configuration cat 3600.

has a table-map at the beginning setting several DSCP values to 0.

map from 46 to 0

followed by a traffic class with ef as matching condition.

match dscp ef

is this supposed to work?

this depends solely on the order of command processing.

thanks!

[M02@rt37 · Accepted solution]

Hello @hurgazoid 

In the QoS config you're working with, the table-map at the beginning is resetting DSCP values, including DSCP 46 (EF), to 0, which means that any packet originally marked with EF will now have its DSCP value changed before further processing.

Since the table-map executes first, this modification happens prior to any classification or policy actions being applied. When the subsequent traffic class attempts to match DSCP EF (46), it will not find any traffic because the DSCP value has already been set to 0 by the table-map. Therefore, the traffic class with the condition to match DSCP EF will not work as expected. To resolve this, you'd need to either reorder the QoS configuration to classify and act on DSCP EF before resetting the value to 0 or adjust the table-map to avoid modifying DSCP 46 if you need to maintain EF for specific policy actions.

This behavior depends entirely on the sequence in which the QoS commands are processed, and with the current order, the class-map will fail to match any EF-marked traffic.

[hurgazoid · Accepted solution]

thanks!