Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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.