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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter20 Co nf iguring QoS
Configuring QoS
This example shows how to define the DSCP-to-DSCP-mutation map. All the entries that are not
explicitly configured are not modified (remains as specified in the null map):
Switch# configure terminal
Switch(config)# mls qos map dscp-mutation mutation1 1 2 3 4 5 6 7 to 0
Switch(config)# mls qos map dscp-mutation mutation1 8 9 10 11 12 13 to 10
Switch(config)# mls qos map dscp-mutation mutation1 20 21 22 to 20
Switch(config)# mls qos map dscp-mutation mutation1 30 31 32 33 34 to 30
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# mls qos trust dscp
Switch(config-if)# mls qos dscp-mutation mutation1
Switch(config-if)# end
Switch# show mls qos maps dscp-mutation mutation1
Dscp-dscp mutation map:
mutation1:
d1 : d2 0 1 2 3 4 5 6 7 8 9
---------------------------------------
0 : 00 00 00 00 00 00 00 00 10 10
1 : 10 10 10 10 14 15 16 17 18 19
2 : 20 20 20 23 24 25 26 27 28 29
3 : 30 30 30 30 30 35 36 37 38 39
4 : 40 41 42 43 44 45 46 47 48 49
5 : 50 51 52 53 54 55 56 57 58 59
6 : 60 61 62 63
Note In the above DSCP-to-DSCP-mutation map, the mutated values are sh own in the body of the matrix.
The d1 column specifies the most-significant digit of the original DSCP; the d2 row specifies the
least-significant digit of the original DSCP. The intersection of the d1 and d2 values provides the
mutated value. For example, a DSCP value of 12 corresponds to a m utate d valu e of 10 .
Configuring Egress Queues on Gigabit-Capable Ethernet Ports
This section describes how to configure the egress queues on Gigabi t-c apa ble Ether net po rts. For
information on configuring 10/100 Ethernet ports, see “Configuring Egress Qu eu es on 10/100 Ethernet
Ports” section on page 20-51.
Depending on the complexity of your network and your QoS solution, you might need to perform all of
the tasks in the next sections. You will need to make decisions about these characteristics:
•Which packets are assigned (by CoS value) to each queue?
•How much of the available buffer space (limit) is allotted to each queue?
•What drop percentage thresholds apply to each queue and whic h D SCP v alue s m ap t o e ach
threshold?
•Is one of the queues the expedite (high-priority) egress queue?
•How much of the available bandwidth is allotted to each queue?
This section contains this configuration information:
•Mapping CoS Values to Select Egress Queues, page 20-45
•Configuring the Egress Queue Size Ratios, page 20-46
•Configuring Tail-Drop Threshold Percentages, page 20-47
•Configuring WRED Drop Thresholds Percentages, page 20-48
•Configuring the Egress Expedite Queue, page 20-50
•Allocating Bandwidth among Egress Queues, page 20-50