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Fixed MAC address: After learning an ARP entry, the AR1200-S does not allow the
modification of the MAC address that is performed through ARP entry learning until this
ARP entry ages. The AR1200-S prevents ARP entries of authorized users from being
modified without permission.
The fixed MAC address methods have two modes: fixed-mac and fixed-all. In fixed-mac
mode, MAC addresses cannot be modified, but VLANs and interfaces can be modified. In
fixed-all mode, MAC addresses, VLANs, and interfaces cannot be modified.
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send-ack: The AR1200-S does not modify an ARP entry immediately when it receives an
ARP packet requesting for modifying a MAC address. Instead, the AR1200-S sends a
unicast packet for acknowledgement to the user matching this MAC address in the original
ARP table.
Defense Against ARP Gateway Attacks
An ARP gateway attack means that an attacker sends gratuitous ARP packets with the source
IP address as the bogus gateway address on a local area network (LAN). After receiving these
packets, the host replaces its gateway address with the address of the attacker. As a result, none
of the hosts on a LAN can access the network.
When the AR1200-S receives ARP packets with the bogus gateway address, the following
situations can occur:
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The source IP address in the ARP packets is the same as the IP address of the interface that
receives the packets.
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The source IP address in the ARP packets is the virtual IP address of the inbound interface
but the source MAC address of ARP packets is not the virtual MAC address of the Virtual
Router Redundancy Protocol (VRRP) group when the VRRP group is in virtual MAC
address mode.
In the preceding situations, the AR1200-S generates ARP anti-attack entries and discards the
packets in a period (the default value is three minutes). This can prevent ARP packets with the
bogus gateway address from being broadcast in a VLAN.
To ensure that packets sent by hosts on the internal network are forwarded to the gateway or to
prevent malicious users from intercepting these packets, the AR1200-S sends gratuitous ARP
packets at a specified interval to update the gateway address in ARP entries of the hosts.
Source Address-based ARP Packet Suppression
When a large number of packets are sent from a source IP address, the CPU resources of the
AR1200-S and the bandwidth reserved for sending ARP packets are occupied.
The AR1200-S can limit the rate of ARP packets with a specified source IP address. If the number
of ARP packets with a specified source IP address received by the AR1200-S within a specified
period exceeds the threshold, the AR1200-S does not process the excessive ARP request packets.
Source Address-based ARP Miss Packet Suppression
When a host sends a large number of IP packets with unreachable destination IP addresses to
attack the device, the AR1200-S suppresses the ARP Miss packets with the specified source IP
address.
If a large number of IP packets whose destination IP address cannot be resolved are sent to the
AR1200-S from a source IP address, the ARP Miss packets are triggered. The AR1200-S collects
Huawei AR1200-S Series Enterprise Routers
Configuration Guide - Security
6 ARP Security Configuration
Issue 02 (2012-03-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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