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Unreasonable configuration of DHCP cause STA can't get the ip

Publication Date:  2017-10-31 Views:  679 Downloads:  0

Issue Description

The scenario is in certain area, there are a lot of users connected to indoor AP. Average 17 STA per AP. Each users have based speed 5M. And there are peak hour, some of the users hard to get connected and need to wait non-peak hour ( e.g. 4am) to get connected and do download things.

Topology is:


Alarm Information

A large number of wireless users cant receive an IP address by DHCP


Handling Process

1 customer user the DHCP servers, we check the ip pool find the there have many free address.

2 trace both from the switch and the ap find dhcp packtes drop random

3 check the accress switch configuration,found there have command of dhcp snooping.

4 check the accress switch dhcp snooping table found DHCP snooping binding table is Exhausted in the access switch

<ACCESS_SWITCH_01>display dhcp snooping               

 DHCP snooping global running information :

DHCPv4 snooping                          : Enable  

 DHCPv6 snooping                          : Enable  

 Static user max number                   : 256    

 Current static user number               : 0       

 Dhcp user max number                     : 256      (default)

Current dhcp user number                 : 256    

 Arp dhcp-snooping detect                 : Disable  (default)

Alarm threshold                          : 100      (default)

Check dhcp-rate                          : Disable  (default)

Dhcp-rate limit(pps)                     : 100      (default)

Alarm dhcp-rate                          : Disable  (default)

Alarm dhcp-rate threshold                : 100      (default)

Discarded dhcp packets for rate limit    : 0      

 Bind-table autosave                      : Disable  (default)

Offline remove mac-address               : Disable  (default)

Client position transfer allowed         : Enable   (default)


DHCP snooping running information for interface GigabitEthernet0/0/1 :

DHCP snooping                            : Enable  

 Trusted interface                        : No     

 Dhcp user max number                     : 256      (default)

Current dhcp and nd user number          : 15     

 Check dhcp-giaddr                        : Disable  (default)

Check dhcp-chaddr                        : Disable  (default)

Alarm dhcp-chaddr                        : Disable  (default)

Root Cause

DHCP snooping binding table is Exhausted in the access switch


Configuration the command “dhcp snooping enable no-user-binding” from the all of the access switch


for WLAN users not need configuration the dhcp snooping from the access switch, because from the AP already enable this.