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Apply QoS to ports or VLANs:
2.
(interface) mls qos vlan-based
By default, QoS is port-based (no mls qos vlan-based) or applied to individual Layer
2 ports. QoS policies can be applied to a port's VLAN instead. When the application
is changed, any port-based QoS policies are detached from the port.
Classify traffic based on a port.
3.
Tip A switch port can be configured to always trust selected inbound QoS parameters in
this step. Otherwise, a QoS policy can be defined to trust QoS parameters conditionally.
This is done in Step 6 (COS) and Step 8 (IOS). On an IOS switch, the trust state can be set
only on physical switch ports and not on VLAN interfaces.
a. (Optional) Set the default ingress CoS value:
(interface) mls qos cos cos-value
The CoS value is set to cos-value (0 to 7, default 0) for frames received on
untrusted ports and for unmarked frames received on trusted ports (frames in the
802.1Q native VLAN).
b. (Optional) Don't trust any inbound information:
(interface) no mls qos trust
The inbound CoS, DSCP, and IP precedence values are not trusted. All these val-
ues are reclassified based on any matching QoS policies or maps. If no policies
are present, both the CoS and DSCP are set to 0.
When QoS is enabled, the default state for each port is untrusted.
c. (Optional) Trust the inbound CoS value by default.
Map CoS values to internal DSCP values:
■
(global) mls qos map cos-dscp dscp1 ... dscp8
The CoS values (0 to 7) from inbound frames are mapped to the correspon-
ding 8 dscp1 through dscp8 values (0 to 63). The resulting internal DSCP
values are then used by the QoS processes in the switch. The default map-
ping is as follows:
CoS
DSCP
0
0 ("best effort")
1
8 (AF class 1 "best effort")
2
16 (AF class 2 "best effort")
3
24 (AF class 3 "best effort")
4
32 (AF class 4 "best effort")
5
40 (EF "best effort")
6
48 (Internetwork control "best effort")
7
56 (Network control "best effort")
Chapter 13: Quality of Service 229
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