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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter34 Configuring Network Security with ACLs
Configuring IPv4 ACLs
For example, if you apply this ACL to an interface:
permit tcp source source-wildcard destination destination-wildcard range 5 60
permit tcp source source-wildcard destination destination-wildcard range 15 160
permit tcp source source-wildcard destination destination-wildcard range 115 1660
permit tcp source source-wildcard destination destination-wildcard
And if this message appears:
ACLMGR-2-NOVMR: Cannot generate hardware representation of access list [chars]
The flag-related operators are not available. To avoid this issue,
•Move the fourth ACE before the first ACE by using ip access-list resequence global configuration
command:
permit tcp source source-wildcard destination destination-wildcard
permit tcp source source-wildcard destination destination-wildcard range 5 60
permit tcp source source-wildcard destination destination-wildcard range 15 160
permit tcp source source-wildcard destination destination-wildcard range 115 1660
or
•Rename the ACL with a name or number that alphanumerically precedes the other ACLs (for
example, rename ACL 79 to ACL 1).
You can now apply the first ACE in the ACL to the interface. The switch allocates the ACE to available
mapping bits in the Opselect index and then allocates flag-related operators to use the same bits in the
TCAM.
Router ACLs function as follows:
•The hardware controls permit and deny actions of standard and extended ACLs (input and output)
for security access control.
•If log has not been specified, the flows that match a deny statement in a security ACL are dropped
by the hardware if ip unreachables is disabled. The flows matching a permit statement are switched
in hardware.
•Adding the log keyword to an ACE in a router ACL causes a copy of the packet to be sent to the
CPU for logging only. If the ACE is a permit statement, the packet is still switched and routed
in hardware.
IPv4 ACL Configuration Examples
This section provides examples of configuring and applying IPv4 ACLs. For detailed information about
compiling ACLs, see the Cisco IOS Security Configuration Guide, Release 12.2 and to the Configuring
IP Services” section in the “IP Addressing and Services” chapter of the Cisco IOS IP Configuration
Guide, Release 12.2.
Figure 34-3 shows a small networked office environment with routed Port 2 connected to Server A,
containing benefits and other information that all employees can access, and routed Port 1 connected to
Server B, containing confidential payroll data. All users can access Server A, but Server B has restricted
access.
Use router ACLs to do this in one of two ways:
•Create a standard ACL, and filter traffic coming to the server from Port 1.
•Create an extended ACL, and filter traffic coming from the server into Port 1.