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Page 15 | AlliedWare Plus™ OS: Overview of QoS
Note that there is just a single mark-dscp map for the whole switch—separate class maps do
not have separate mark-dscp maps.
The configuration required to use the mark-dscp map is a little more complex than the
configuration for setting the values explicitly.
1. First, write entries into the mark-dscp map table.
This is a matter of specifying the DSCP, CoS, queue, and/or bandwidth class to associate
with the given pair of DSCP and bandwidth class values. To do this, enter the command:
awplus(config)#mls qos map mark-dscp <0-63> to [new-dscp <0-63>] [new-cos
<0-7>] [new-queue <0-7>] [new-bandwidth-class {green|yellow|red}]
Use this command to populate those entries of the map that you will be using. For
example, to ensure that traffic that arrives with a DSCP of 34 gets marked to bandwidth
class green, queue 4 and CoS 4, enter the command:
awplus(config)#mls qos map mark-dscp 34 to new-cos 4 new-queue 4
new-bandwidth-class green
In this example, we do not change the DSCP value—it stays as 34.
2. Set the class map to use the mark-dscp map.
Enter the commands:
awplus(config)#policy-map <name>
awplus(config-pmap)#class <name>
awplus(config-pmap-c)#trust dscp
The trust dscp command indicates that this class map will use the mark-dscp map for pre-
marking.
Note that you can’t use the command trust dscp at the same time as the commands set
cos, set queue, or set bandwidth-class. This is because you can’t combine using the
mark-dscp map with explicitly setting premarking values.
3. Decide how the class map will choose the DSCP value to use in looking up entries in the
mark-dscp map.
There are two choices:
z use the DSCP value that is present in each packet. This means that values marked into
a packet will depend on the DSCP value already present in the packet at ingress.
This choice requires no further configuration—the default behaviour is to use the
DSCP value present in each packet.
z specify a single DSCP value that QoS will use for look-ups for all packets that match
the class map.
To configure this choice, use the set dscp command.
Note that the meaning of the set dscp command changes when you use the command
trust dscp on a class map. When trust dscp has been configured, set dscp specifies
the DSCP value for QoS to use to perform look-ups into the mark-dscp map. If trust
dscp has not been configured on the class map, the set dscp command specifies the
DSCP value that will be marked into all packets that match the class map (as described
in "Setting new values explicitly" on page 14).