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Using VACLs with Cisco IOS ACLs
To display the percentage of ACL storage that is being used, enter the show security acl resource-usage
Note
command.
These sections provide the Cisco IOS ACL and VACL configuration guidelines and examples:
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Using the Implicit Deny Action
If possible, use the implicit deny action at the end of an ACL (deny any any) and define the ACEs to
permit only allowed traffic. You can achieve this same effect by defining all the deny entries and
specifying permit ip any any at the end of the list (see
Grouping Actions Together
To define multiple actions in an ACL (permit, deny, redirect), group each action type.
page 15-20
in line 6 was grouped with the permit actions. If this deny action is removed, the result of merging would
be 53 entries, instead of 329 entries.
Limiting the Number of Actions
An ACL with only the permit ACEs has two actions: permit and deny (because of the implicit deny at
the end of the list). An ACL with permit and redirect has three actions: permit, redirect, and deny
(because of the implicit deny at the end of the list).
When configuring an ACL, the best merge results are obtained when you specify only two different
actions: permit and deny, redirect and permit, or redirect and deny.
With supervisor engine software release 7.1(1) or later releases, due to an improved algorithm for
Note
merging ACLs, you do not need to limit the number of actions when configuring an ACL.
To specify a redirect and deny ACL, do not use any permit ACEs. To specify a redirect and permit ACL,
use permit ACEs, redirect ACEs, and for the last ACE, specify permit ip any any. If you specify permit
ip any any, you will override the implicit deny ip any at the end of the list (see
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
15-18
Using the Implicit Deny Action, page 15-18
Grouping Actions Together, page 15-18
Limiting the Number of Actions, page 15-18
Avoiding Layer 4 Port Information, page 15-19
Estimating Merge Results with Supervisor Engine Software Releases Prior to Release 7.1(1),
page 15-19
Estimating Merge Results with Supervisor Engine Software Releases 7.1(1) or Later Releases,
page 15-21
shows what can happen when you do not group each type. In the example, the deny action
Chapter 15
Configuring Access Control
Example 1, page
15-20).
Example 4, page
Example 3,
15-21).
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