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Configuration Guide - IP Service

CloudEngine 8800, 7800, 6800, and 5800 V200R003C00

This document describes the configurations of IP Service, including IP address, ARP, DHCP, DNS, IP performance optimization, IPv6, DHCPv6, and IPv6 DNS.
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Disabling Learning of ARP Entries on Different Network Segments

Disabling Learning of ARP Entries on Different Network Segments

Background

You can choose to enable or disable the function of learning ARP entries on different network segments based on service access and network security requirements. On the network shown in Figure 2-15, to allow Device1 and Device3 to communicate, routed ARP proxy needs to be enabled on Device2.
  1. Device1 sends an ARP request packet to request for the MAC address of Device3.
  2. Upon receipt of the ARP request packet, Device2 discovers that the route destined for the IP address 10.2.2.1 is reachable and meets the requirement for routed proxy. Then, Device2 replies with an ARP response packet in which the source IP address is 10.2.2.1 and the source MAC address (2–2–2) corresponds to the interface receiving the ARP request packet.
  3. Upon receipt of the ARP response packet, Device1 does not perform validity check on the source IP address. Instead, Device1 performs MAC address learning and then sends Device3 a packet with the destination MAC address as 2–2–2. In this manner, Device1 and Device3 properly communicate through Device2.
Figure 2-15 ARP entry learning on different network segments

By default, the main physical interface of a device supports the function of learning ARP entries of IP addresses on different network segments, and the routed ARP proxy can access devices on different network segments. This function is by default disabled on logical interfaces and Layer 3 sub-interfaces.

This, however, may pose the device to risks. For example, if a network attacker on the same network segment sends a large number of ARP request packets based on the false source IP address, ARP entries of the device may be used up. After the function of learning ARP entries on different network segments is disabled, the physical interface checks the source IP address of the received ARP packet. If the source IP address is on a different network segment, the physical interface does not perform ARP entry learning, protecting the device from attacks.

You can choose to disable the function of learning ARP entries of IP addresses on different network segments on a specified physical interface based on service access and network security requirements.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run the arp learning on-different-segment disable command to disable the function of learning ARP entries on different network segments.

    By default, the function of learning ARP entries on different network segments is enabled.

    After this command is run, the device cannot learn ARP entries of the IP addresses on different network segments. However, the ARP entries of the IP addresses on different network segments that have learned before this configuration are still valid until the aging period of ARP entries ends.

  3. Run commit

    The configuration is committed.

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Updated: 2019-05-08

Document ID: EDOC1100004354

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