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Configuration Guide - Security

CloudEngine 8800, 7800, 6800, and 5800 V200R005C10

This document describes the configurations of Security, including ACL, local attack defense, MFF, attack defense, traffic suppression and storm control, ARP security, Port security, DHCP snooping, ND snooping, PPPoE+, IPSG, SAVI, separating the management plane from the service plane, security risks.
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Gratuitous ARP Packet Discarding

Gratuitous ARP Packet Discarding

In a gratuitous ARP packet, the source and destination IP addresses are both the local IP address, the source MAC address is the local MAC address, and the destination MAC address is a broadcast address. When a user host connects to a network, the host broadcasts a gratuitous ARP packet to notify other devices on the network of its MAC address and to check whether any device uses the same IP address as its own IP address in the broadcast domain. When the MAC address of a user host changes, the host sends a gratuitous ARP packet to notify all hosts before its ARP entry cached on other user hosts ages out.

Any user host can send gratuitous ARP packets without being authenticated. This causes the following problems:
  • If a large number of gratuitous ARP packets are broadcast on the network, network devices cannot process valid ARP packets due to CPU overload.
  • If a device processes bogus gratuitous ARP packets, ARP entries are updated incorrectly, leading to communication interruptions.

To solve the preceding problems, enable the gratuitous ARP packet discarding function on the gateway.

If the gratuitous ARP packet discarding function is enabled on the gateway, other hosts on the network cannot update their ARP entries when a host uses a new MAC address to connect to the network. Consequently, other hosts cannot communicate with this host. When a host changes the interface card and restarts, or the standby node takes over the active node due to faults in a two-node cluster hot backup system, MAC addresses on the network are changed.

Updated: 2019-04-20

Document ID: EDOC1100074765

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