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Cisco ASDM User Guide
OL-16647-01
Chapter 30 Configuring ARP Inspection and Bridging Parameters
Configuring ARP Inspection
Note The dedicated management interface, if present, never floods packets even if this parameter
is set to flood.
ARP inspection prevents malicious users from impersonating other hosts or routers (known as ARP
spoofing). ARP spoofing can enable a “man-in-the-middle” attack. For example, a host sends an
ARP request to the gateway router; the gateway router responds with the gateway router MAC address.
The attacker, however, sends another ARP response to the host with the attacker MAC address instead
of the router MAC address. The attacker can now intercept all the host traffic before forwarding it on to
the router.
ARP inspection ensures that an attacker cannot send an ARP response with the attacker MAC address,
so long as the correct MAC address and the associated IP address are in the static ARP table.
Fields
Interface—Shows the interface names.
ARP Inspection Enabled—Shows if ARP inspection is enabled, Yes or No.
Flood Enabled—If ARP inspection is enabled, shows if the action is to flood unknown packets, Yes
or No. If ARP inspection is disabled, this value is always No.
Edit—Edits the ARP inspection parameters for the selected interface.
Modes
The following table shows the modes in which this feature is available:
Edit ARP Inspection Entry
The Edit ARP Inspection Entry dialog box lets you set ARP inspection settings.
Fields
Enable ARP Inspection—Enables ARP inspection.
Flood ARP Packets—Specifies that packets that do not match any element of a static ARP entry are
flooded out all interfaces except the originating interface. If there is a mismatch between the MAC
address, the IP address, or the interface, then the security appliance drops the packet. If you do not
check this check box, all non-matching packets are dropped.
Note The default setting is to flood non-matching packets. To restrict ARP through the security
appliance to only static entries, then set this command to no-flood.
The Management 0/0 interface or subinterface, if present, never floods packets even if this
parameter is set to flood.
Firewall Mode Security Context
Routed Transparent Single
Multiple
Context System
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