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CLI-based Configuration Guide - Security

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document provides the basic concepts, configuration procedures, and configuration examples in different application scenarios of the network management feature supported by the device.
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(Optional) Configuring the Device to Discard DHCP Request Messages When GIADDR Field Is Not 0

(Optional) Configuring the Device to Discard DHCP Request Messages When GIADDR Field Is Not 0

Context

The gateway IP address (GIADDR) field in a DHCP Request message records the IP address of the first DHCP relay agent through which the DHCP Request message passes. When a DHCP client sends a DHCP Request message, if the DHCP server and client are on different network segments, the first DHCP relay agent fills its own IP address in the GIADDR field before forwarding the DHCP Request message. The DHCP server then uses the IP address in this field to locate the DHCP client and select an appropriate address pool from which to assign an IP address to the client.

To ensure that the device obtains parameters such as MAC addresses for generating a binding table, enable DHCP snooping on Layer 2 access devices or the first DHCP relay agent. This ensures that the GIADDR field in the DHCP Request messages received by the DHCP snooping-enabled device is 0. If the GIADDR field is not 0, the message is considered to be invalid and discarded.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Enable the device to check whether the GIADDR field in the DHCP Request message is 0 in the VLAN view or interface view.
    1. Run vlan vlan-id

      The VLAN view is displayed.

      Or run interface interface-type interface-number

      The interface view is displayed.

    2. Run dhcp snooping check dhcp-giaddr enable

      The device is enabled to check whether the GIADDR field in a DHCP Request message is 0.

      By default, the device does not check whether the GIADDR field in a DHCP Request message is 0.

    If you run this command in the VLAN view, the command takes effect on all the DHCP messages in the specified VLAN received by all the interfaces on the device. If you run this command in the interface view, the command takes effect on all the DHCP messages received by the specified interface.

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Updated: 2019-05-20

Document ID: EDOC1100034077

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