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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 26 Configuring Network Security with ACLs
Understanding ACLs
•
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 IPv4 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 IPv4 packets are
filtered by the router ACL. Other packets are not filtered.
•
When a VLAN map, input router ACL, and input port ACL exist in an SVI, incoming packets
received on the ports to which a port ACL is applied are only filtered by the port ACL. Incoming
routed IPv4 packets received on other ports are filtered by both the VLAN map and the router ACL.
Other packets are filtered only by the VLAN map.
•
When a VLAN map, 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 only filtered by the port ACL. Outgoing
routed IPv4 packets are filtered by both the VLAN map and the router ACL. Other packets are
filtered only by the VLAN map.
Port ACLs
Port ACLs are ACLs that are applied to Layer 2 interfaces on a switch. Port ACLs are supported only on
physical interfaces and not on EtherChannel interfaces and you can apply them only in the inbound
direction. You cannot apply an ACL to a port configured with a service instance.
These access lists are supported on Layer 2 interfaces:
•
Standard IP access lists using source addresses
•
Extended IP access lists using source and destination addresses and optional protocol type
information
•
MAC extended access lists using source and destination MAC addresses and optional protocol type
information
The switch examines ACLs associated with all inbound features configured on a given interface and
permits or denies packet forwarding based on how the packet matches the entries in the ACL. In this way,
ACLs are used to control access to a network or to part of a network.
Figure 26-1
is an example of using
port ACLs to control access to a network when all workstations are in the same VLAN. ACLs applied at
the Layer 2 input would allow Host A to access the Human Resources network, but prevent Host B from
accessing the same network. Port ACLs can only be applied to Layer 2 interfaces in the inbound
direction.
