3com 5500-ei pwr Installation Instruction

 

1-2 

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config: where rules in an ACL are matched in the order defined by the user. 

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auto: where rules in an ACL are matched in the order determined by the system, 

namely the “depth-first” rule (Layer 2 ACLs and user-defined ACLs do not support this 

feature). 

For depth-first rule, there are two cases: 

1)  Range of source IP address: The smaller the source IP address range (that is, the more 

the number of zeros in the wildcard mask), the higher the match priority. 

2)  Fragment keyword: A rule with the fragment keyword is prior to others.  

3)  If the above two conditions are identical, the earlier configured rule applies.  

1)  Protocol range: A rule which has specified the types of the protocols carried by IP is 

prior to others.  

2)  Range of source IP address: The smaller the source IP address range (that is, the more 

the number of zeros in the wildcard mask), the higher the match priority. 

3)  Range of destination IP address. The smaller the destination IP address range (that is, 

the more the number of zeros in the wildcard mask), the higher the match priority. 

4)  Range of Layer 4 port number, that is, TCP/UDP port number. The smaller the range, 

the higher the match priority. 

5)  Number of parameters: the more the parameters, the higher the match priority. 

If rule A and rule B are still the same after comparison in the above order, the weighting 

principles will be used in deciding their priority order. Each parameter is given a fixed 

weighting value. This weighting value and the value of the parameter itself will jointly 

decide the final matching order. Involved parameters with weighting values from high to 

low are icmp-type, established, dscp, tos, precedence, fragment. Comparison rules are 

listed below. 

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The smaller the weighting value left, which is a fixed weighting value minus the 

weighting value of every parameter of the rule, the higher the match priority. 

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If the types of parameter are the same for multiple rules, then the sum of parameters’ 

weighting values of a rule determines its priority. The smaller the sum, the higher the 

match priority. 

In the switch, an ACL can be directly applied to hardware for packet filtering and traffic 

classification. In this case, the rules in an ACL are matched in the order determined by the 

hardware instead of that defined in the ACL. For Switch 5500-EI series, the later the rule 

applies, the higher the match priority.  

ACLs are directly applied to hardware when they are used for: 

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Implementing QoS