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CLI-based Configuration Guide - IP Service

AR100, AR120, AR160, AR1200, AR2200, AR3200, and AR3600 V300R003

This document describes the concepts and configuration procedures of IP Service features on the device, and provides the configuration examples.
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Static ARP

Static ARP

Definition

Static ARP allows a network administrator to create fixed mapping between IP and MAC addresses. Static ARP entries will not be aged or overridden by dynamic ARP entries.

Category

Static ARP entries are classified into short and long entries.
  • Short static ARP entries: The network administrator creates the mapping between IP and MAC addresses without specifying the VLAN and outbound interface.

    If the outbound interface is a Layer 2 Ethernet interface, short static ARP entries cannot be directly used to forward packets. Before sending a packet, the device sends an ARP Request packet. If the source IP and MAC addresses in the received ARP Reply packet are the same as those in the configured static ARP entry, the device adds the VLAN and interface that receive the ARP Reply packet to this static ARP entry. The device can use this static ARP entry to forward subsequent packets.

  • Long static ARP entries: The network administrator creates mapping between IP and MAC addresses, and also specifies the VLAN and outbound interface through which the device sends packets.

    Long static ARP entries are directly used to forward packets. Therefore, long static ARP entries are recommended.

Usage Scenario

In normal cases, devices on a network can use ARP to dynamically learn ARP entries, and age or update the generated dynamic ARP entries. However, when a network encounters an ARP attack, the dynamic ARP entries may be incorrectly updated or aged. As a result, the communication between authorized users becomes abnormal. Static ARP entries will not be aged or overridden by dynamic ARP entries, ensuring communication security. If a static ARP entry is configured on a device, the device can communicate with the peer device using only the specified MAC address. Network attackers cannot modify the mapping between the IP and MAC addresses using ARP packets, ensuring communication between the two devices. Static ARP entries are configured on gateways.

Static ARP entries apply to the following scenarios:
  • Networks with important devices such as servers: Network attackers cannot update the ARP entries containing IP addresses of important devices on the router using ARP attack packets, ensuring communication between users and important devices.
  • Networks on which MAC addresses of user devices are multicast MAC addresses: By default, a device does not learn ARP entries when receiving the ARP packets whose source MAC addresses are multicast MAC addresses.
  • Scenario in which a network administrator wants to prevent a certain IP address from accessing devices: The network administrator binds the IP address to an unavailable MAC address.
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Updated: 2019-03-06

Document ID: EDOC1100069333

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