Cisco Catalyst 2960 Series, Configuration Manual

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• A Layer 2 interface can have only one MAC access list. If you apply a MAC access list to a Layer 2
interface that has a MAC ACL configured, the new ACL replaces the previously configured one.
The mac access-group interface configuration command is only valid when applied to a physical Layer 2
interface. You cannot use the command on EtherChannel port channels.
Note
IP Access List Entry Sequence Numbering
• This feature does not support dynamic, reflexive, or firewall access lists.
Information About Configuring IPv4 Access Control Lists
ACL Overview
Packet filtering can help limit network traffic and restrict network use by certain users or devices. ACLs filter
traffic as it passes through a router or switch and permit or deny packets crossing specified interfaces or
VLANs. An ACL is a sequential collection of permit and deny conditions that apply to packets. When a packet
is received on an interface, the switch compares the fields in the packet against any applied ACLs to verify
that the packet has the required permissions to be forwarded, based on the criteria specified in the access lists.
One by one, it tests packets against the conditions in an access list. The first match decides whether the switch
accepts or rejects the packets. Because the switch stops testing after the first match, the order of conditions
in the list is critical. If no conditions match, the switch rejects the packet. If there are no restrictions, the switch
forwards the packet; otherwise, the switch drops the packet. The switch can use ACLs on all packets it forwards,
including packets bridged within a VLAN.
You configure access lists on a router or Layer 3 switch to provide basic security for your network. If you do
not configure ACLs, all packets passing through the switch could be allowed onto all parts of the network.
You can use ACLs to control which hosts can access different parts of a network or to decide which types of
traffic are forwarded or blocked at router interfaces. For example, you can allow e-mail traffic to be forwarded
but not Telnet traffic. ACLs can be configured to block inbound traffic, outbound traffic, or both.
Standard and Extended IPv4 ACLs
This section describes IP ACLs.
An ACL is a sequential collection of permit and deny conditions. One by one, the switch tests packets against
the conditions in an access list. The first match determines whether the switch accepts or rejects the packet.
Because the switch stops testing after the first match, the order of the conditions is critical. If no conditions
match, the switch denies the packet.
The software supports these types of ACLs or access lists for IPv4:
• Standard IP access lists use source addresses for matching operations.
• Extended IP access lists use source and destination addresses for matching operations and optional
protocol-type information for finer granularity of control.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Information About Configuring IPv4 Access Control Lists