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Configuration Guide - Security

S7700 and S9700 V200R011C10

This document describes the configurations of Security, including ACL, reflective ACL, local attack defense, MFF, attack defense, traffic suppression and storm control, ARP security, port security, DHCP snooping, ND snooping, PPPoE+, IPSG, SAVI, URPF, keychain, separating the management plane from the service plane, security risks.
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Strict ARP Learning

Strict ARP Learning

If many user hosts simultaneously send a large number of ARP packets to a device, or attackers send bogus ARP packets to the device, the following problems occur:

  • Processing ARP packets consumes many CPU resources. The device learns many invalid ARP entries, which exhaust ARP entry resources and prevent the device from learning ARP entries for ARP packets from authorized users. Consequently, communication of authorized users is interrupted.

  • After receiving bogus ARP packets, the device incorrectly modifies the ARP entries. As a result, authorized users cannot communicate with one another other.

To avoid the preceding problems, configure the strict ARP learning function on the gateway.

After the strict ARP learning function is enabled, the device learns only ARP entries for ARP reply packets in response to ARP Request packets that it has sent. In this way, the device can defend against most ARP attacks.

Figure 7-3  Strict ARP learning

As shown in Figure 7-3, after receiving an ARP Request packet from UserA, the gateway sends an ARP Reply packet to UserA and adds or updates an ARP entry matching UserA. After the strict ARP learning function is enabled on the gateway:
  • The gateway does not add or update an ARP entry for userA when it receives an ARP Request packet from UserA. If the ARP Request packet requests the MAC address of the gateway, the gateway sends an ARP Reply packet to UserA.

  • The gateway adds or updates an ARP entry matching UserB if it sends an ARP Request packet to UserB, after it receives the ARP Reply packet.

Updated: 2019-10-18

Document ID: EDOC1000178319

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