Assigning a DSCP policy on the basis of the DSCP in IPv4 packets received from upstream devices
The preceding section describes how to forward a policy set by an edge (or upstream) switch. This option changes a DSCP policy in an IPv4 packet by changing its IP ToS codepoint and applying the priority associated with the new codepoint. (A DSCP policy consists of a differentiated services codepoint and an associated 802.1p priority.) You can use this option concurrently with the diffserv 802.1p priority option (above), as long as the DSCPs specified in the two options do not match.
To use this option to configure a change in policy:
Syntax:
qos type-of-service diff-services
Enables ToS Diff-serve QoS so that Diff-serve policy configurations can be applied to incoming packets that have matching codepoints.
Syntax:
qos type-of-service diff-services <current-codepoint> dscp <new-codepoint>
Configures the switch to select an incoming IP packet carrying the
<current-codepoint>
and then use the
<new-codepoint>
to assign a new, previously configured DSCP policy to the packet. The policy overwrites the
<current-codepoint>
with the
<new-codepoint>
and assigns the 802.1p priority specified by the policy.
Syntax:
no qos type-of-service
Disables all ToS classifier operation. Current ToS DSCP policies and priorities remain in the configuration and will become available if you re-enable ToS Diff-services.
Syntax:
no qos type-of-service [diff-services <codepoint>]
Deletes the DSCP policy assigned to the
<codepoint>
and returns the
<codepoint>
to the 802.1p priority setting it had before the DSCP policy was assigned, which is either a value from 0 - 7 or
No-override.
Syntax:
show qos type-of-service
Displays a listing of codepoints with any corresponding DSCP policy reassignments for outbound packets. Also displays the 802.1p priority for each codepoint that does not have a DSCP remarking policy assigned to it.
Example
Received DSCP |
Policy DSCP |
802.1p Priority |
Policy Name (Optional) |
|---|---|---|---|
001100 |
17 |
6 |
Level 6 |
001101 |
16 |
4 |
Level 4 |
Determine whether the DSCPs already have priority assignments, which could indicate use by existing applications. This is not a problem as long as the configured priorities are acceptable for all applications using the same DSCP. (See Note on changing a priority setting. Also, a DSCP must have a priority configured before you can assign any QoS classifiers to use it. See Differentiated Services Codepoint (DSCP) mapping.)
After configuring the DSCP policies for the codepoints you want to use, assign the policies to the codepoints in the selected packet type.
An example of policy assignment to outbound packets on the basis of the DSCP in the packets received from upstream devices is shown below. The specified DSCP policies overwrite the original DSCPs on the selected packets, and use the 802.1p priorities previously configured.
switch(config)# qos type-of-service diff-services 001100 dscp 17 switch(config)# qos type-of-service diff-services 001101 dscp 16 switch(config)# show qos type-of-service Type of Service : Differentiated Services Codepoint DSCP Policy | Priority --------- ----------- + ----------- 000000 | No-override 000001 | No-override 000010 | No-override 000011 | No-override 000100 | No-override 000101 | No-override 000110 | No-override 000111 | No-override 001000 001011 | 7 001001 | No-override 001010 | 1 001011 | 7 001100 010001 | 6 001101 010000 | 4