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Catalyst 3560 Switch Software Configuration Guide
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Chapter 33 Configuring Network Security with ACLs
Configuring IPv4 ACLs
After you create an ACL, any additions are placed at the end of the list. You cannot selectively add ACL
entries to a specific ACL. However, you can use no permit and no deny access-list configuration mode
commands to remove entries from a named ACL. This example shows how you can delete individual
ACEs from the named access list border-list:
Switch(config)# ip access-list extended border-list
Switch(config-ext-nacl)# no permit ip host 10.1.1.3 any
Being able to selectively remove lines from a named ACL is one reason you might use named ACLs
instead of numbered ACLs.
After creating a named ACL, you can apply it to interfaces (see the “Applying an IPv4 ACL to an
Interface” section on page 33-19) or to VLANs (see the “Configuring VLAN Maps” section on
page 33-29).
Using Time Ranges with ACLs
You can selectively apply extended ACLs based on the time of day and the week by using the
time-range global configuration command. First, define a time-range name and set the times and the
dates or the days of the week in the time range. Then enter the time-range name when applying an ACL
to set restrictions to the access list. You can use the time range to define when the permit or deny
statements in the ACL are in effect, for example, during a specified time period or on specified days of
the week. The time-range keyword and argument are referenced in the named and numbered extended
ACL task tables in the previous sections, the “Creating Standard and Extended IPv4 ACLs” section on
page 33-7, and the “Creating Named Standard and Extended ACLs” section on page 33-14.
These are some of the many possible benefits of using time ranges:
• You have more control over permitting or denying a user access to resources, such as an application
(identified by an IP address/mask pair and a port number).
• You can control logging messages. ACL entries can be set to log traffic only at certain times of the
day. Therefore, you can simply deny access without needing to analyze many logs generated during
peak hours.
Time-based access lists trigger CPU activity because the new configuration of the access list must be
merged with other features and the combined configuration loaded into the TCAM. For this reason, you
should be careful not to have several access lists configured to take affect in close succession (within a
small number of minutes of each other.)
Note The time range relies on the switch system clock; therefore, you need a reliable clock source. We
recommend that you use Network Time Protocol (NTP) to synchronize the switch clock. For more
information, see the “Managing the System Time and Date” section on page 7-1.
Beginning in privileged EXEC mode, follow these steps to configure a time-range parameter for an
ACL:
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 time-range time-range-name Assign a meaningful name (for example, workhours) to the time range to
be created, and enter time-range configuration mode. The name cannot
contain a space or quotation mark and must begin with a letter.