Administrator Guide

Determining the Order in Which ACLs are Used to Classify
Traffic
When you link class-maps to queues using the service-queue command, the system matches the class-
maps according to queue priority (queue numbers closer to 0 have lower priorities).
For example, as described in the previous example, class-map cmap2 is matched against ingress packets
before
cmap1.
ACLs acl1 and acl2 have overlapping rules because the address range 20.1.1.0/24 is within 20.0.0.0/8.
Therefore (without the keyword order), packets within the range 20.1.1.0/24 match positive against cmap1
and are buffered in queue 4, though you intended for these packets to match positive against cmap2 and be
buffered in queue 1.
In cases such as these, where class-maps with overlapping ACL rules are applied to different queues, use the
keyword order. The Dell Networking OS writes to the CAM ACL rules with lower order numbers (order
numbers closer to 0) before rules with higher order numbers so that packets are matched as you intended.
• Specify the order in which you want to apply ACL rules using the keyword order.
order
The order can range from 0 to 254.
By default, all ACL rules have an order of 255.
Setting DSCP Values for Egress Packets Based on Flow
Match-any Layer 3 flows may have several match criteria. All flows that match at least one of the match
criteria are mapped to the same queue because they are in the same class map.
Setting a DSCP value from QOS-POLICY-IN mode (refer to Setting a DSCP Value for Egress Packets) assigns
the same DSCP value to all of the matching flows in the class-map.
The flow-based DSCP marking feature allows you to assign different DSCP to each match criteria.
• Create matching flows within a class map that have different DSCP values.
CLASS MAP mode
match set-ip-dscp
The values you set from CLASS-MAP mode override the value you set in the QoS input policy DSCP value.
Packets matching the rule are marked with the specified value.
Example of Marking Flows in the Same Queue with Different DSCP Values
Dell#show run class-map
!
class-map match-any example-flowbased-dscp
match ip access-group test set-ip-dscp 2
match ip access-group test1 set-ip-dscp 4
match ip precedence 7 set-ip-dscp 1
Dell#show run qos-policy-input
!
qos-policy-input flowbased
set ip-dscp 3
Quality of Service (QoS) 737