Quality of Service (QoS)
©2008 Allied Telesis Inc. All rights reserved.
Software Version 5.2.1
AlliedWare Plus
TM
Operating System Software Reference C613-50003-00 REV E
39.11
Premarking your Traffic
Premarking relates to adding QoS markers to your incoming data traffic. Network switches will
often be configured with two different premarking profiles, one for the QoS edge switches and
another for the QoS core switches. This situation would apply If you are operating DSCP
domains.
QoS markers can be applied at both the link layer (within the CoS field), and at the network
layer (within the DSCP field). For more information on this topic see
“QoS Packet
Information” on page 39.3
.
For boundary
QoS switches
Traffic entering QoS boundary switches is unlikely to contain pre-existing QoS tagging. In this
case, you can apply one or more of the following QoS mapping options.
■
Assign an output queue to data associated with a particular class-map
(using the
set queue
command) and apply it to the input (
ingress)
port.
■
Assign a CoS tag to data associated with a particular class-map,
Using the
set cos
command. You can then map the CoS tag to an output (egress) port
queue (using the
CoS to egress queue premarking
command).
■
Assign a DSCP tag to data associated with a particular class-map (using the
set dscp
command). Alternatively, you can use the
trust dscp
command to map the DSCP tag to
an egress port queue, a CoS value, or both. At the premarking stage you can set this
mapping using the command,
mls qos map mark-dscp to
.
After policing, you can then use
the remarking command
mls qos map policed-dscp to
in order to reassign a particular
DSCP to a specific egress queue, CoS value, or both.
When no other mapping is set, all traffic is sent to the queue that is set by the
mls qos queue
command. If this command is unset (i.e. in the absence of any other queue selection) traffic will
be sent to queue 2.
For core
QoS switches
Traffic entering ports within the QoS core network will almost certainly contain some pre-
existing QoS tagging. Where this is the case, you can apply one of the following QoS mapping
options.
■
Map the CoS tag to an egress queue. You can do this either for the whole switch or for
specific ports via their assigned policy-maps. See
“CoS to egress queue premarking” on
page 39.11
.
■
Map the DSCP tag to an output queue. You can do this either for the whole switch or for
specific ports via their assigned policy-maps. See “When no other mapping is set, all traffic
is sent to the queue that is set by the
mls qos queue
command. If this command is unset
DSCP to egress queue mapping” on page 1.12.
■
Remap incoming data DSCP or CoS tags to values that are more appropriate for a
particular switch or network.
CoS to egress queue premarking
If you are using CoS tagging for your QoS functions, your traffic is likely to be either entering
the switch with a pre existing CoS tag, or will have appropriate tags attached via your class-
maps and policy-maps. You can now mark the data for a particular egress queue, which will
take effect when the data reaches its output port. There are two fundamental methods of
applying CoS tagged packets to egress queues:
1.
Apply a global mapping of CoS tags to egress queues for all ports.
2.
Apply a CoS to egress queue mapping for the class-map / policy-map. This mapping -
which forms part of the policy map - is applied at an input port, but will take effect at the
