User's Manual

24-55
24.3 Prevent ARP, ND Spoofing Example
Equipment Explanation
Equipment
Configuration
Quality
switch
IP:192.168.2.4; IP:192.168.1.4; mac: 00-00-00-00-00-04
1
A
IP:192.168.2.1; mac: 00-00-00-00-00-01
1
B
IP:192.168.1.2; mac: 00-00-00-00-00-02
1
C
IP:192.168.2.3; mac: 00-00-00-00-00-03
some
There is a normal communication between B and C on above diagram. A wants switch to forward packets
sent by B to itself, so need switch sends the packets transfer from B to A. firstly A sends ARP reply packet to
switch, format is: 192.168.2.3, 00-00-00-00-00-01, mapping its MAC address to C’s IP, so the switch changes
IP address when it updates ARP list., then data packet of 192.168.2.3 is transferred to 00-00-00-00-00-01
address (A MAC address).
In further, a transfers its received packets to C by modifying source address and destination address, the
mutual communicated data between B and C are received by A unconsciously. Because the ARP list is update
timely, another task for A is to continuously send ARP reply packet, and refreshes switch ARP list.
So it is very important to protect ARP list, configure to forbid ARP learning command in stable environment,
and then change all dynamic ARP to static ARP, the learned ARP will not be refreshed, and protect for users.
Switch#config
Switch(config)#interface vlan 1
Switch(Config-If-Vlan1)#arp 192.168.2.1 00-00-00-00-00-01 interface eth 1/0/2
Switch(Config-If-Vlan1)#interface vlan 2
Switch(Config-If-Vlan2)#arp 192.168.1.2 00-00-00-00-00-02 interface eth 1/0/2
Switch(Config-If-Vlan2#interface vlan 3
Switch(Config-If-Vlan3)#arp 192.168.2.3 00-00-00-00-00-03 interface eth 1/0/2
Switch(Config-If-Vlan3)#exit
Switch(Config)#ip arp-security learnprotect
Switch(Config)#
Switch(config)#ip arp-security convert
A B
C
Switch