Trust Boundaries; Class Of Behavior - Cisco Nexus 9000 Series Configuration Manual

Trust Boundaries

Marking Feature
QoS group
Ingress
CoS
Trust Boundaries
The trust boundary forms a perimeter on your network. Your network trusts (and does not override) the
markings on your switch.
The incoming interface enforces the trust boundary as follows:
• All Fibre Channel and virtual Fibre Channel interfaces are automatically classified into the FCoE system
• By default, all Ethernet interfaces are trusted interfaces. A packet tagged with an 802.1p class of service
• Any packet not tagged with an 802.1p CoS value is classified into the default drop system class. If the
• You can override the default untagged CoS value for an Ethernet interface or port channel.
After the system applies the correct CoS value to an untagged packet, QoS treats the packet according to the
newly defined class.

Class of Behavior

For routed unicast traffic, the CoS value is derived from the 3 most-significant bits (3 MSB) of the Differentiated Services Code Point
(DSCP) value. For bridged unicast traffic, the CoS value is copied from the CoS value received in the 802.1q header. Note that on
Layer 2 access links there is no trunk header. Therefore, if traffic is received on an access port and bridged, it will egress the switch
with CoS 0. The DSCP value does not change, but the packet may not get the desired priority. You can manually set the CoS value
in a policy-map via any QoS policy that manually sets the CoS or DSCP value.
Routed multicast traffic derives its CoS value similar to routed unicast traffic. For bridged multicast traffic, the behavior depends on
the Layer 3 state. If there is no Layer 3 state for the multicast group, the CoS is derived similar to the bridged unicast traffic. If there
is a Layer 3 state for the multicast group, the CoS is derived similar to routed unicast traffic.
Note When you enable Protocol Independent Multicast (PIM) in sparse mode on the switch virtual interface
(SVI) for the VLAN in which traffic is received, PIM creates an S,G entry for any multicast traffic.
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class.
(CoS) value is classified into a system class using the value in the packet.
untagged packet is sent over a trunk, it is tagged with the default untagged CoS value, which is zero.
Description
Locally significant QoS values that can be
manipulated and matched within the system. The
range is from 0 to 3.
Status of the marking applies to incoming packets.
Layer 2 VLAN ID
Configuring Marking