Quality of Service (QoS): Managing Bandwidth More Effectively
Using QoS Classifiers To Configure Quality of Service for Outbound Traffic
3400cl/6400cl Switch Restriction. On the 3400cl and 6400cl switches,
“mixing” ToS DSCP policies and 802.1p priorities is not recommended. Refer
to the Note on page
8-10.
For more on DSCP, refer to “Terminology” on page 8-5.
Steps for Creating a Policy Based on VLAN-ID Classifier.
1. Determine the VLAN-ID classifier to which you want to assign a DSCP
policy.
2. Determine the DSCP policy for packets carrying the selected VLAN-ID:
a. Determine the DSCP you want to assign to the selected packets. (This
codepoint will be used to overwrite the DSCP carried in packets
received from upstream devices.)
b. Determine the 802.1p priority you want to assign to the DSCP.
3. Configure the DSCP policy by using qos dscp-map to configure the priority
for each codepoint. (For details, see the example later in this section, and
to
“Differentiated Services Codepoint (DSCP) Mapping” on page 8-62.)
Note A codepoint must have an 802.1p priority (0 - 7) before you can configure the
codepoint for use in prioritizing packets by VLAN-ID. If a codepoint you want
to use shows No-override in the Priority column of the DSCP Policy table (show
qos dscp-map), then assign a priority before proceeding.
4. Configure the switch to assign the DSCP policy to packets with the
specified VLAN-ID.
Syntax: qos dscp-map < codepoint > priority < 0 - 7 >
This command is optional if a priority has already
been assigned to the < codepoint >. The command creates
a DSCP policy by assigning an 802.1p priority to a
specific DSCP. When the switch applies this priority to
a packet, the priority determines the packet’s queue in
the outbound port to which it is sent. If the packet leaves
the switch on a tagged port, it carries the 802.1p
priority with it to the next downstream device. If the
packet is IPv4, the packet’s DSCP will be replaced by the
codepoint specified in this command. (Default: For
most codepoints,
No-override. See figure 8-14 on page 8-
63 on page 8-63.)
8-54
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