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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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DHCP Clients Cannot Go Online Due to DHCP Snooping

DHCP Clients Cannot Go Online Due to DHCP Snooping

Fault Description

The possible causes are as follows:
  • The network-side interface connected to the DHCP server is not configured as the trusted interface.
  • The number of DHCP clients connected to the user-side interface has reached the maximum value.

Procedure

  1. Check whether the trusted interface is correctly configured.
    1. Run the display dhcp snooping configuration command to check in which VLANs and on which interfaces DHCP snooping is enabled and whether "Trusted interface" is displayed on the network-side interface.

      NOTE:

      After DHCP snooping is enabled on an interface, the interface is an untrusted interface by default. When receiving messages from the network-side interfaces, the device processes only the DHCP Reply messages received on the trusted interface and discards those on untrusted interfaces. When receiving messages from user-side interfaces, the device forwards the messages only to the trusted interface.

    2. Check whether the network-side interface on the DHCP server is the trusted interface. If it is not the trusted interface, run the dhcp snooping trusted command in the VLAN or interface view to configure the interface as a trusted interface.
  2. If the interface is correctly configured, check whether the number of access DHCP clients reaches the threshold.
    1. Run the display dhcp snooping configuration command to check whether "DHCP user max number: XX" is displayed globally, in the VLAN or on the user-side interface.

      NOTE:

      If "DHCP user max number: XX" is not displayed, the default maximum number of DHCP clients is 512. The configured value takes preference.

      If you set the maximum value in the system view, VLAN view, and the interface view, the smallest value takes effect.

    2. Run the display dhcp snooping user-bind all command to view the number of dynamic DHCP snooping entries on the DHCP snooping-enabled interface. If the number of entries on the interface has reached the maximum value, new DHCP clients cannot access the network.
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Updated: 2019-08-07

Document ID: EDOC1100034077

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