For wired or wireless ports that are connected to the
(end points such as IP phones, laptops,
cameras, telepresence units, or other devices), their DSCP, precedence, or CoS
values coming in from these end points are trusted by the
and therefore are retained in the absence
of any explicit policy configuration.
This trust behavior
is applicable to both upstream and downstream QoS.
The packets are
enqueued to the appropriate queue per the default initial configuration. No
priority queuing at the
is done by default. This is true for
unicast and multicast packets.
In scenarios where
the incoming packet type differs from the outgoing packet type, the trust
behavior and the queuing behavior are explained in the following table. Note
that the default trust mode for a port is DSCP based. The trust mode ‘falls
back’ to CoS if the incoming packet is a pure Layer 2 packet. You can also
change the trust setting from DSCP to CoS. This setting change is accomplished
by using an MQC policy that has a class default with a 'set cos cos table
default default-cos' action, where default-cos is the name of the table map
created (which only performs a default copy).
Table 10. Trust and Queueing
Behavior
Incoming
Packet
|
Outgoing
Packet
|
Trust Behavior
|
Queuing
Behavior
|
Layer 3
|
Layer 3
|
Preserve
DSCP/Precedence
|
Based on DSCP
|
Layer 2
|
Layer 2
|
Not applicable
|
Based on CoS
|
Tagged
|
Tagged
|
Preserve DSCP
and CoS
|
Based on DSCP
(trust DSCP takes precedence)
|
Layer 3
|
Tagged
|
Preserve DSCP,
CoS is set to 0
|
Based on DSCP
|
The Cisco IOS XE 3.2 Release supported different trust
defaults for wired and wireless ports. The trust default for wired ports was
the same as for this software release. For wireless ports, the default system
behavior was non-trust, which meant that when the
came up, all markings for the wireless
ports were defaulted to zero and no traffic received priority treatment. For
compatibility with an existing wired
, all traffic went to the best-effort queue
by default. The access point performed priority queuing by default. In the
downstream direction, the access point maintained voice, video, best-effort,
and background queues for queuing. The access selected the queuing strategy
based on the 11e tag information. By default, the access point treated all
wireless packets as best effort.
The
default trust behavior in the case of wireless ports could be changed by using
the
qos
wireless
default
untrust command.
Note |
If you upgrade from
Cisco IOS XE 3.2 SE Release to a later release, the default behavior of the
wireless traffic is still untrusted. In this situation, you can use the
no
qos
wireless-default untrust command to enable trust
behavior for wireless traffic. However, if you install Cisco IOS XE 3.3 SE or a
later release on the
device, the default QoS behavior for wireless
traffic is trust. Starting with Cisco IOS XE 3.3 SE Release and later, the
packet markings are preserved in both egress and ingress directions for new
installations (not upgrades) for wireless traffic.
|