Some Users Cannot Obtain IP Addresses after DHCP Snooping Is Enabled

Procedure

1. Check whether the number of access DHCP users has reached the threshold.
   1. Run the display dhcp snooping [ interface interface-type interface-number | vlan vlan-id ] command to check whether "Dhcp user max number: XX" is displayed globally, in the VLAN, or on the user-side interface.

      By default, the maximum number of DHCP snooping binding entries that can be learned on an interface is 512 for S2720-EI, 2048 for S5720-LI, S5735-L, S5735S-L, S5735S-L-M, S5720S-LI, S5720-SI, S5735-S, S5735S-S, S5735-S-I, S5720I-SI, S5720S-SI, S5730-SI, S5730S-EI, S6720-LI, S6720S-LI, S6720-SI, and S6720S-SI, and 8192 for other models.

   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.

      To increase the maximum value of DHCP access users, run the dhcp snooping max-user-number max-number command.

2. If the number of access DHCP users has not reached the threshold, check whether the transmission rate of DHCP messages has exceeded the upper limit.
   1. Run the display dhcp snooping [ interface interface-type interface-number | vlan vlan-id ] command to check whether "Dhcp-rate limit(pps): xx" is displayed globally, in the VLAN, or on the user-side interface.

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

   2. If DHCP users cannot access the network because the DHCP snooping rate limit is low, run the dhcp snooping check dhcp-rate rate command in the system view, interface view, and VLAN view to increase the rate limit values.