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Chapter 22
Configuring Dynamic ARP Inspection
Configuring Dynamic ARP Inspection in DHCP Environments
This procedure shows how to configure dynamic ARP inspection when two switches support this feature.
Host 1 is connected to Switch A, and Host 2 is connected to Switch B as shown in
page
A DHCP server is connected to Switch A. Both hosts acquire their IP addresses from the same DHCP
server. Therefore, Switch A has the bindings for Host 1 and Host 2, and Switch B has the binding for
Host 2.
Dynamic ARP inspection depends on the entries in the DHCP snooping binding database to verify
Note
IP-to-MAC address bindings in incoming ARP requests and ARP responses. Make sure to enable DHCP
snooping to permit ARP packets that have dynamically assigned IP addresses. For configuration
information, see
For information on how to configure dynamic ARP inspection when only one switch supports the
feature, see the
Beginning in privileged EXEC mode, follow these steps to configure dynamic ARP inspection. You must
perform this procedure on both switches. This procedure is required.
Command
Step 1
show cdp neighbors
Step 2
configure terminal
Step 3
ip arp inspection vlan vlan-range
Step 4
interface interface-id
Step 5
ip arp inspection trust
Step 6
end
78-16180-02
22-3. Both switches are running dynamic ARP inspection on VLAN 1 where the hosts are located.
Chapter 21, "Configuring DHCP Features and IP Source Guard."
"Configuring ARP ACLs for Non-DHCP Environments" section on page
Purpose
Verify the connection between the switches.
Enter global configuration mode.
Enable dynamic ARP inspection on a per-VLAN basis. By
default, dynamic ARP inspection is disabled on all VLANs.
For vlan-range, specify 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 4094.
Specify the same VLAN ID for both switches.
Specify the interface connected to the other switch, and enter
interface configuration mode.
Configure 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 simply 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. The
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. For
more information, see the
on page
22-12.
Return to privileged EXEC mode.
Catalyst 3750 Switch Software Configuration Guide
Configuring Dynamic ARP Inspection
Figure 22-2 on
22-8.
"Configuring the Log Buffer" section
22-7
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