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Cisco IE 2000 Switch Software Configuration Guide
OL-25866-01
Chapter 26 Configuring Dynamic ARP Inspection
How to Configure Dynamic ARP Inspection
Configuring ARP ACLs for Non-DHCP Environments
This procedure shows how to configure DAI when Switch B shown in Figure 26-2 on page 26-3 does not
support DAI or DHCP snooping.
If you configure port 1 on Switch A as trusted, a security hole is created because both Switch A and
Host 1 could be attacked by either Switch B or Host 2. To prevent this possibility, you must configure
port 1 on Switch A as untrusted. To permit ARP packets from Host 2, you must set up an ARP ACL and
apply it to VLAN 1. If the IP address of Host 2 is not static (it is impossible to apply the ACL
configuration on Switch A) you must separate Switch A from Swit ch B at Layer 3 and use a router to
route packets between them.
Step 3 ip arp inspection vlan vlan-range Enables DAI on a per-VLAN basis. By default, DAI is disabled
on all VLANs.
vlan-range—Specifies a single VLAN identified by VLAN ID
number, a range of VLANs separated by a hyphen, or a series of
VLANs separated by a comma. The range is 1 to 4096.
Specifies the same VLAN ID for both switches.
Step 4 interface interface-id Specifies the interface connected to the other switch, and enters
interface configuration mode.
Step 5 ip arp inspection trust Configures the connection between the switches as trusted.
By default, all interfaces are untrusted.
The switch does not check ARP packets that it receives from the
other switch on the trusted interface; it only forwards the
packets.
For untrusted interfaces, the switch intercepts all ARP requests
and responses. It verifies that the intercepted packets have valid
IP-to-MAC address bindings before updating the local cache and
before forwarding the packet to the appropriate destination. Th e
switch drops invalid packets and logs them in the log buffer
according to the logging configuration specified with the ip arp
inspection vlan logging global configuration command.
Step 6 end Returns to privileged EXEC mode.
Command Purpose
Command Purpose
Step 1 configure terminal Enters global configuration mode.
Step 2 arp access-list acl-name Defines an ARP ACL, and enters ARP access-list configuration
mode. By default, no ARP access lists are defined.
Note At the end of the ARP access list, there is an implicit
deny ip any mac any command.