Dear Nicolas,
one of the limitations in VSX is the lack of the QoS rule in individual Virtual Systems. So, if you migrate a Firewall rulebase from a Security Management Server into a Multi-Domain Server, you will notice that the QoS rules are gone.
However, on the VS0 context, you can create QoS rules for prioritizing packets in which the ToS Byte is marked with DSCP values. This is only applicable for external packets hitting the external interface of your VSX Gateway.
The syntax is:
cpqos class add HighPrio type reg weight 1000 prio 15 dscp 64 (for packets with the DSCP value of 00100010)
cpqos class add MediumPrio type reg weight 500 prio 7 dscp 18
cpqos class add LowPrio type reg weight 100 prio 2 dscp default
cpqos install (?)
You will find the policy here: $FWDIR/database/qos_policy.C.
Cheers,
Yasushi