HP 6120G/XG HP ProCurve Series 6120 Blade Switches Access Security Guide - Page 339
Note on Implicit, The Packet-Filtering Process in an ACL with, Entries ACEs
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IPv4 Access Control Lists (ACLs) ACL Operation N o t e o n I m p l i c i t For ACLs configured to filter inbound packets, note that Implicit Deny filters Deny any packets, including those with a DA specifying the switch itself. This operation helps to prevent management access from unauthorized IP sources. Test a packet against criteria in first ACE. Is there a match? Yes Perform action (permit or deny). No Test the packet against criteria in second ACE. Is there a match? No Yes Perform action (permit or deny). Test packet against criteria in Nth ACE. 1. If a match is not found with the first ACE in an ACL, the switch proceeds to the next ACE and so on. 2. If a match with an explicit End ACE is subsequently found, the packet is either permit ted (forwarded) or denied (dropped), depending on the action specified in the matching ACE. In this case the switch ignores all sub sequent ACEs in the ACL. 3. If a match is not found with any explicit ACE in the ACL, End the switch invokes the implicit deny any at the end of every ACL, and drops the packet. Note: If the list includes a permit any entry, no packets can reach the implicit deny any at the end of the list. Is there a match? Yes Perform action (permit or deny). End No Deny the packet End (invoke implicit deny any). Figure 9-3. The Packet-Filtering Process in an ACL with N Entries (ACEs) For example, suppose you want to configure an ACL on the switch (with an ID of "100") to invoke these policies: 1. Permit all inbound traffic on port 12 sent from IP address 11.11.11.42. 9-15
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