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HAPTER
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| Security Measures
ARP Inspection
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Figure 201: Showing ACL Statistics
ARP INSPECTION
ARP Inspection is a security feature that validates the MAC Address
bindings for Address Resolution Protocol packets. It provides protection
against ARP traffic with invalid MAC-to-IP address bindings, which forms
the basis for certain “man-in-the-middle” attacks. This is accomplished by
intercepting all ARP requests and responses and verifying each of these
packets before the local ARP cache is updated or the packet is forwarded to
the appropriate destination. Invalid ARP packets are dropped.
ARP Inspection determines the validity of an ARP packet based on valid
IP-to-MAC address bindings stored in a trusted database – the DHCP
snooping binding database (see "DHCP Snooping Configuration" on
page 411). This database is built by DHCP snooping if it is enabled on
globally on the switch and on the required VLANs. ARP Inspection can also
validate ARP packets against user-configured ARP access control lists
(ACLs) for hosts with statically configured addresses (see "Configuring
an ARP ACL" on page 365).
COMMAND USAGE
Enabling & Disabling ARP Inspection
◆ ARP Inspection is controlled on a global and VLAN basis.
◆ By default, ARP Inspection is disabled both globally and on all VLANs.
■
If ARP Inspection is globally enabled, then it becomes active only on
the VLANs where it has been enabled.
■
When ARP Inspection is enabled globally, all ARP request and reply
packets on inspection-enabled VLANs are redirected to the CPU and
their switching behavior handled by the ARP Inspection engine.
■
If ARP Inspection is disabled globally, then it becomes inactive for
all VLANs, including those where inspection is enabled.
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