Rate Limiting on ARP Miss Messages

When a user host sends a large number of IP packets with unresolvable destination IP addresses to attack a network device (the device has a route to the destination IP address of a packet but has no ARP entry matching the next hop of the route), the device generates a large number of ARP Miss messages. IP packets (ARP Miss packets), which trigger ARP Miss messages, are sent to the control board for processing. The device generates and delivers many temporary ARP entries according to the ARP Miss messages, and sends a large number of ARP Request packets to the destination network. This increases CPU usage of the device and consumes considerable network bandwidth. As shown in Figure 10-1, the attacker sends IP packets with the unresolvable destination IP address 10.2.1.5/24 to the gateway.

Figure 10-1 ARP Miss

To avoid the preceding problems, the device takes measures to limit the rate of ARP Miss messages.

• Limiting the rate of ARP Miss messages based on source IP addresses

  If the number of ARP Miss messages triggered by IP packets and sent from a source IP address per second exceeds the limit, the device considers that an attack has been initiated by this source IP address.

  If a source IP address is specified, the rate of ARP Miss messages triggered by IP packets from this source IP address is limited. If no source IP address is specified, the rate of ARP Miss messages triggered by IP packets from any source IP address is limited.

• Limiting the rate of ARP Miss messages globally, in a VLAN, or on an interface

  If rate limit on ARP Miss messages is configured in the system view, VLAN view, and interface view, the device uses the configurations in the interface view, VLAN view, and system view in order.

  • Limiting the rate of ARP Miss messages globally: limits the number of ARP Miss messages processed on the entire device.

  • Limiting the rate of ARP Miss messages in a VLAN: limits the number of ARP Miss messages processed on all interfaces in a VLAN. The configuration in a VLAN does not affect IP packet forwarding on interfaces in other VLANs.

  • Limiting the rate of ARP Miss messages on an interface: limits the number of ARP Miss messages processed on an interface. The configuration on an interface does not affect IP packet forwarding on other interfaces.

• Limiting the rate of ARP Miss messages by setting the aging time of temporary ARP entries

  When IP packets trigger ARP Miss messages, the device generates temporary ARP entries and sends ARP Request packets to the destination network.

  • In the aging time of temporary ARP entries:
    • Before receiving an ARP reply packet, the device discards the IP packets matching the temporary ARP entry and does not generate ARP Miss messages.
    • After receiving an ARP Reply packet, the device generates a correct ARP entry to replace the temporary entry.
  • When temporary ARP entries age out, the device clears them. If no ARP entry matches the IP packets forwarded by the device, ARP Miss messages and temporary ARP entries are repeatedly generated.

  When a device undergoes an ARP Miss attack, you can extend the aging time of temporary ARP entries and reduce the frequency of triggering ARP Miss messages to mitigate the impact on the device.