Assigning a DSCP policy based on VLAN-ID
This option assigns a previously configured DSCP policy (codepoint and 802.1p priority) to outbound IP packets having the specified VLAN-ID (VID). The switch performs the following:
- Selects an incoming IP packet on the basis of the VLAN-ID it carries.
- Overwrites the packet’s DSCP with the DSCP configured in the switch for such packets.
- Assigns 802.1p priority configured in the switch for the new DSCP (see Differentiated Services Codepoint (DSCP) mapping).
- Forwards the packet through the appropriate outbound port queue.
Steps for creating a policy based on VLAN-ID classifier:
-
Determine the VLAN-ID classifier to which you want to assign a DSCP policy.
-
Determine the DSCP policy for packets carrying the selected VLAN-ID:
-
Determine the DSCP you want to assign to the selected packets. (This codepoint will be used to overwrite the DSCP carried in packets received through the source-port from upstream devices.)
-
Determine the 802.1p priority you want to assign to the DSCP.
-
-
Configure the DSCP policy by using
qos dscp-map
to configure the priority for each codepoint (see Differentiated Services Codepoint (DSCP) mapping for more information). -
Configure the switch to assign the DSCP policy to packets with the specified VLAN-ID.
Syntax:
vlan <vid> qos dscp <codepoint>
Assigns a DSCP policy to packets carrying the specified VLAN-ID, and overwrites the DSCP in these packets with the assigned
<codepoint>
value. This policy includes an 802.1p priority and 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 downstream device.
(Default:
No-override
)
Syntax:
no vlan <vid> qos
Removes QoS classifier for the specified VLAN.
Syntax:
show qos vlan-priority
Displays a listing of the QoS VLAN-ID classifiers currently in the running-config file.
VLAN-ID |
DSCP |
Priority |
---|---|---|
40 |
15 |
7 |
30 |
16 |
5 |
20 |
17 |
1 |
1 |
17 |
1 |
switch(config)# vlan 1 qos dscp 17 switch(config)# vlan 20 qos dscp 17 switch(config)# vlan 30 qos dscp 16 switch(config)# vlan 40 qos dscp 15 switch(config)# show qos vlan-priority VLAN priorities VLAN ID Apply rule | DSCP Priority ------- ----------- + ------ ----------- 1 DSCP | 010001 1 20 DSCP | 010001 1 30 DSCP | 010000 5 40 DSCP | 001111 7
-
Overwrite the original DSCPs in the selected packets with the new DSCPs specified in the above policies.
-
Assign the 802.1p priorities in the above policies to the appropriate packets.