ARP Entry Fixing
To defend against ARP gateway spoofing attacks, configure the ARP entry fixing function on a gateway. After the gateway with this function enabled learns an ARP entry for the first time, it does not modify the ARP entry, but only updates part of the entry, or sends a unicast ARP Request packet to check the validity of the ARP packet for updating the entry.
The device supports three ARP entry fixing modes, as described in Table 10-3.
Mode |
Description |
---|---|
fixed-all |
When receiving an ARP packet, the device discards the packet if the MAC address, interface number, or VLAN ID does not match an ARP entry. This mode applies to networks where user MAC addresses and user access locations are fixed. |
fixed-mac |
When receiving an ARP packet, the device discards the packet if the MAC address does not match the MAC address in the corresponding ARP entry. If the MAC address in the ARP packet matches that in the corresponding ARP entry while the interface number or VLAN ID does not match that in the ARP entry, the device updates the interface number or VLAN ID in the ARP entry. This mode applies to networks where user MAC addresses are unchanged but user access locations often change. |
send-ack |
When the device receives ARP packet A with a changed MAC address, interface number, or VLAN ID, it does not immediately update the corresponding ARP entry. Instead, the device sends a unicast ARP Request packet to the user with the IP address mapped to the original MAC address in the ARP entry, and then determines whether to change the MAC address, VLAN ID, or interface number in the ARP entry depending on the response from the user.
This mode applies to networks where user MAC addresses and user access locations often change. |