C H A P T E R 31 Configuring Network Security With Acls; Supported Acls - Cisco WS-C3750-48PS-S Software Configuration Manual

Understanding ACLs
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.
An ACL contains an ordered list of access control entries (ACEs). Each ACE specifies permit or deny
and a set of conditions the packet must satisfy in order to match the ACE. The meaning of permit or deny
depends on the context in which the ACL is used.
The switch supports IP ACLs and Ethernet (MAC) ACLs:
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This switch also supports quality of service (QoS) classification ACLs. For more information, see the
"Classification Based on QoS ACLs" section on page
This section includes information on these topics:
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Supported ACLs

The switch supports three applications of ACLs to filter traffic:
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You can use input port ACLs, router ACLs, and VLAN maps on the same switch. However, a port ACL
takes precedence over a router ACL or VLAN map.
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Catalyst 3750 Switch Software Configuration Guide
31-2
IP ACLs filter IP traffic, including TCP, User Datagram Protocol (UDP), Internet Group
Management Protocol (IGMP), and Internet Control Message Protocol (ICMP).
Ethernet ACLs filter non-IP traffic.
Supported ACLs, page 31-2
Handling Fragmented and Unfragmented Traffic, page 31-5
ACLs and Switch Stacks, page 31-6
Port ACLs access-control traffic entering a Layer 2 interface. The switch does not support port ACLs
in the outbound direction. You can apply only one IP access list and one MAC access list to a Layer
2 interface.
Router ACLs access-control routed traffic between VLANs and are applied to Layer 3 interfaces in
a specific direction (inbound or outbound).
VLAN ACLs or VLAN maps access-control all packets (bridged and routed). You can use VLAN
maps to filter traffic between devices in the same VLAN. VLAN maps are configured to provide
access-control based on Layer 3 addresses for IP. Unsupported protocols are access-controlled
through MAC addresses using Ethernet ACEs. After a VLAN map is applied to a VLAN, all packets
(routed or bridged) entering the VLAN are checked against the VLAN map. Packets can either enter
the VLAN through a switch port or through a routed port after being routed.
When both an input port ACL and a VLAN map are applied, incoming packets received on ports
with a port ACL applied are filtered by the port ACL. Other packets are filtered by the VLAN map
When an input router ACL and input port ACL exist in an switch virtual interface (SVI), incoming
packets received on ports to which a port ACL is applied are filtered by the port ACL. Incoming
routed IP packets received on other ports are filtered by the router ACL. Other packets are not
filtered.
When an output router ACL and input port ACL exist in an SVI, incoming packets received on the
ports to which a port ACL is applied are filtered by the port ACL. Outgoing routed IP packets are
filtered by the router ACL. Other packets are not filtered.
Chapter 31 Configuring Network Security with ACLs
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