The trust boundary is enforced by the incoming interface as follows:
All Fibre Channel and virtual Fibre Channel interfaces are automatically classified into the FCoE system class.
By default, all Ethernet interfaces are trusted interfaces.The 802.1p CoS and DSCP are preserved unless the marking is configured. There is no default CoS to queue and DSCP to queue mapping. You can define and apply a policy to create these mappings. By default, without a user defined policy, all traffic is assigned to the default queue.
Any packet that is not tagged with an 802.1p CoS value is classified into the default drop system class. If the untagged packet is sent over a trunk, it is tagged with the default untagged CoS value, which is zero.
You can override the default untagged CoS value for an Ethernet interface or port channel.
After the system applies the untagged CoS value, QoS functions the same as for a packet that entered the system tagged with the CoS value.