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Cisco ME 3800X and 3600X Switch Software Configuration Guide
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Chapter 26 Configuring Network Security with ACLs
Configuring IPv4 ACLs
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 26-19
) or to VLANs (see the
“Configuring VLAN Maps” section on
page 26-29
).
Using Time Ranges with ACLs
You can selectively apply extended ACLs based on the time of day and 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 26-7
,
and the
“Creating Named Standard and Extended ACLs” section on page 26-14
.
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 5-1
.
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.
