Reference Guide

Quality of Service (QoS) | 725
Figure 40-9. Using the Order Keyword in ACLs
Creating a Layer 2 class map
All class maps are Layer 3 by default; you can create a Layer 2 class map by specifying the option layer2
with the
class-map command. A Layer 2 class map differentiates traffic according to 802.1p value and/or
characteristics defined in a MAC ACL.
1. Create a match-any class map using the command
class-map match-any or a match-all class map using
the command
class-map match-all from CONFIGURATION mode, and enter the keyword layer2.
2. Once you create a class-map, Dell Networking OS places you in CLASS MAP mode. From this mode,
specify your match criteria using the command
match mac. Match-any class maps allow up to five
access-lists, and match-all class-maps allow only one. You can match against only one VLAN ID.
3. After you specify your match criteria, link the class-map to a queue using the command
service-queue
from POLICY MAP mode.
Determining the order in which ACLs are used to classify traffic
When you link class-maps to queues using the command service-queue, Dell Networking OS matches the
class-maps according to queue priority (queue numbers closer to 0 have lower priorities). For example, in
Figure 40-9, 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 7, though you intended for these packets to match positive against cmap2 and be
buffered in queue 4.
In cases such as these, where class-maps with overlapping ACL rules are applied to different queues, use
the
order keyword to specify the order in which you want to apply ACL rules, as shown in Figure 40-9. The
order can range from 0 to 254. 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. By default, all ACL rules have an order of 254.
Dell(conf)#ip access-list standard acl1
Dell(config-std-nacl)#permit 20.0.0.0/8
Dell(config-std-nacl)#exit
Dell(conf)#ip access-list standard acl2
Dell(config-std-nacl)#permit 20.1.1.0/24 order 0
Dell(config-std-nacl)#exit
Dell(conf)#class-map match-all cmap1
Dell(conf-class-map)#match ip access-group acl1
Dell(conf-class-map)#exit
Dell(conf)#class-map match-all cmap2
Dell(conf-class-map)#match ip access-group acl2
Dell(conf-class-map)#exit
Dell(conf)#policy-map-input pmap
Dell(conf-policy-map-in)#service-queue 7 class-map cmap1
Dell(conf-policy-map-in)#service-queue 4 class-map cmap2
Dell(conf-policy-map-in)#exit
Dell(conf)#interface tengig 1/0
Dell(conf-if-te-1/0)#service-policy input pmap