An ACL sequence number is an ordering value assigned to an access control entry (ACE). Cisco IOS commonly numbers the first ACE 10 and increases each following entry by 10, leaving gaps for later entries. section 23.2.1
Reading sequence numbers
A displayed ACL with sequence numbers 10 deny 192.168.1.0 and 20 permit 192.168.0.0 shows that the deny ACE is evaluated before the permit ACE. section 23.2.1
Named ACL configuration lets you specify a sequence number when adding an ACE. For example, sequence number 15 inserts an entry between existing entries 10 and 20, which can change filtering behavior. section 23.2.2
Sequence numbers also support targeted editing in named ACL configuration mode. The command no 30 removes only ACE 30, after which a replacement ACE can be assigned sequence number 30. section 24.3.1
Numbered ACLs edited directly from global configuration mode do not support deleting an individual ACE; using no on an ACE command deletes the entire numbered ACL. Enter ACL configuration mode before using sequence-number editing. section 24.3.1
