IPv4 Access Control Lists (ACLs)

General ACL Operating Notes

General ACL Operating Notes

ACLs do not provide DNS hostname support. ACLs cannot be config­ ured to screen hostname IP traffic between the switch and a DNS.

ACLs Do Not Affect Serial Port Access. ACLs do not apply to the

switch’s serial port.

ACL Screening of IPv4 Traffic Generated by the Switch. ACLs applied on the switch screen IP traffic when other devices generate it. Simi­ larly, ACL applications can screen responses from other devices to unscreened IP traffic the switch generates.

ACL Logging.

The ACL logging feature generates a message only when packets are explicitly denied as the result of a match, and not when explicitly permitted or implicitly denied. To help test ACL logging, configure the last entry in an ACL as an explicit deny statement with a log statement included.

Logging enables you to selectively test specific devices or groups. However, excessive logging can affect switch performance. For this reason, ProCurve recommends that you remove the logging option from ACEs for which you do not have a present need. Also, avoid configuring logging where it does not serve an immediate purpose. (Note that ACL logging is not designed to function as an accounting method.) See also “Apparent Failure To Log All ‘Deny’ Matches” in the section titled “ACL Problems”, found in appendix C, “Troubleshoot­ ing” of the Management and Configuration Guide for your switch.

When configuring logging, you can reduce excessive resource use by configuring the appropriate ACEs to match with specific hosts instead of entire subnets. (For more on resource usage, refer to “Monitoring Shared Resources” on page 9-100.)

Minimum Number of ACEs in an ACL. Any ACL must include at least one ACE to enable IP traffic screening. A numbered ACL cannot be created without at least one ACE. A named ACL can be created “empty”; that is, without any ACEs. However in an empty ACL applied to an interface, the Implicit Deny function does not operate, and the ACL has no effect on traffic.

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