32-10
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter32 Understanding and Configuring Dynamic ARP Inspection
Configuring Dynamic ARP Inspection
Vlan ACL Logging DHCP Logging
---- ----------- ------------
100 Deny Deny#
SwitchB# show ip dhcp snooping binding
MacAddress IpAddress Lease(sec) Type VLAN Interface
------------------ --------------- ---------- ------------- ---- --------------------
00:02:00:02:00:02 170.1.1.2 3492 dhcp-snooping 100 GigabitEthernet3/31
Total number of bindings: 1
SwitchB# show ip arp insp statistics vlan 100
Vlan Forwarded Dropped DHCP Drops ACL Drops
---- --------- ------- ---------- ---------
100 2398 0 0 0
Vlan DHCP Permits ACL Permits Source MAC Failures
---- ------------ ----------- -------------------
100 2398 0 0
Vlan Dest MAC Failures IP Validation Failures Invalid Protocol Data
---- ----------------- ---------------------- ---------------------
100 0 0 0
SwitchB#
Configuring ARP ACLs for Non-DHCP Environments
This procedure shows how to configure dynamic ARP inspection when Switch B shown in Figure 32-3
on page 32-5 does not support dynamic ARP inspection 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 100. If the IP address of Host 2 is not static, such that it is impossible to apply the
ACL configuration on Switch A, you must separate Switch A from Switch B at Layer 3 and use a router
to route packets between them.
To configure an ARP ACL (on switch A in a non-DHCP environment), perform this task:
Command Purpose
Step1 Switch# configure terminal Enters global configuration mode.
Step2 Switch(config)# arp access-list
acl-name
Defines an ARP ACL, and enter 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.