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Dynamic Host Configuration Protocol | 327
View the number of entries in the ARP database with the show arp inspection database command.
Figure 13-8. Command example: show arp inspection database
Use show arp inspection statistics command to see how many valid and invalid ARP packets have been
processed.
Figure 13-9. Command example: show arp inspection database
Bypass the ARP Inspection
You can configure a port to skip ARP inspection by defining the interface as trusted, which is useful in
multi-switch environments. ARPs received on trusted ports bypass validation against the binding table. All
ports are untrusted by default.
Source Address Validation
Using the DHCP binding table, FTOS can perform three types of source address validation (SAV):
• IP Source Address Validation on page 328 prevents IP spoofing by forwarding only IP packets that
have been validated against the DHCP binding table.
Task Command Syntax Command Mode
Specify an interface as trusted so that ARPs are not
validated against the binding table.
arp inspection-trust
INTERFACE
FTOS Behavior: Introduced in FTOS version 8.2.1.0, Dynamic ARP Inspection (DAI) was available for
Layer 3 only. FTOS version 8.2.1.1 extends DAI to Layer 2.
FTOS#show arp inspection database
Protocol Address Age(min) Hardware Address Interface VLAN CPU
----------------------------------------------------------------------------
Internet 10.1.1.251 - 00:00:4d:57:f2:50 Gi 0/2 Vl 10 CP
Internet 10.1.1.252 - 00:00:4d:57:e6:f6 Gi 0/1 Vl 10 CP
Internet 10.1.1.253 - 00:00:4d:57:f8:e8 Gi 0/3 Vl 10 CP
Internet 10.1.1.254 - 00:00:4d:69:e8:f2 Te 0/50 Vl 10 CP
FTOS#
FTOS#show arp inspection statistics
Dynamic ARP Inspection (DAI) Statistics
---------------------------------------
Valid ARP Requests : 0
Valid ARP Replies : 1000
Invalid ARP Requests : 1000
Invalid ARP Replies : 0
FTOS#