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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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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.
  • The transmission rate of DHCP messages has exceeded the upper rate limit, and the DHCP messages from new DHCP clients are being discarded.

Procedure

  1. Check whether the trusted interface is correctly configured.
    1. Run the display dhcp snooping command to check in which VLANs and on which interfaces is DHCP snooping enabled and "Trusted interface" information 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 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 32768. 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 user-bind dhcp snooping 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.
  3. If the number of access DHCP clients does not reach the limit, check whether the transmission rate of DHCP packets exceeds the limit.
    1. Run the display dhcp snooping command to check whether "Rate-limit value(pps): xx" is displayed globally, in the VLAN or on the user-side interface.

      NOTE:

      If "Rate-limit value(pps): xx" is not displayed, the default rate limit is 100 pps. The configured value takes preference.

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

    2. If DHCP clients cannot access the network because the DHCP snooping rate limit is low, run the dhcp snooping rate-limit command in the system view, interface view, and VLAN view to increase the rate limit values.
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Updated: 2019-04-20

Document ID: EDOC1100074765

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