H3C Technologies H3C S12500 Series Switches - Manual (Page 11)

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Match order
The rules in an ACL are sorted in a specific order. When a packet matches a rule, the device stops the
match process and performs the action defined in the rule. If an ACL contains overlapping or conflicting
rules, the matching result and action to take depend on the rule order.
The following ACL match orders are available:
• config—Sorts ACL rules in ascending order of rule ID. A rule with a lower ID is matched before a
rule with a higher ID. If you use this approach, carefully check the rule content and order.
• auto—Sorts ACL rules in depth-first order. Depth-first ordering makes sure any subset of a rule is
always matched before the rule.
Table 1 lists the sequence of tie breakers that depth-first ordering
uses to sort rules for each type of ACL.
The match order of user-defined ACLs can only be config.
Table 1 Sort ACL rules in depth-first order
ACL category Sequence of tie breakers
IPv4 basic ACL
1. VPN instance
2. More 0s in the source IP address wildcard (more 0s means a narrower IP
address range)
3. Smaller rule ID
IPv4 advanced ACL
4. VPN instance
5. Specific protocol type rather than IP (IP represents any protocol over IP)
6. More 0s in the source IP address wildcard mask
7. More 0s in the destination IP address wildcard
8. Narrower TCP/UDP service port number range
9. Smaller rule ID
IPv6 basic ACL
10. Longer prefix for the source IP address (a longer prefix means a narrower IP
address range)
11. Smaller rule ID
IPv6 advanced ACL
12. Specific protocol type rather than IP (IP represents any protocol over IPv6)
13. Longer prefix for the source IPv6 address
14. Longer prefix for the destination IPv6 address
15. Narrower TCP/UDP service port number range
16. Smaller rule ID
Ethernet frame header ACL
17. More 1s in the source MAC address mask (more 1s means a smaller MAC
address)
18. More 1s in the destination MAC address mask
19. Smaller rule ID
A wildcard mask, also called an inverse mask, is a 32-bit binary and represented in dotted decimal
notation. In contrast to a network mask, the 0 bits in a wildcard mask represent ‘do care’ bits, and the 1
bits represent ‘don’t care’ bits. If the 'do care' bits in an IP address are identical to the ‘do care’ bits in
an IP address criterion, the IP address matches the criterion. All ‘don’t care’ bits are ignored. The 0s and
1s in a wildcard mask can be noncontiguous. For example, 0.255.0.255 is a valid wildcard mask.