Qtech QSW-8200-28T-AC — dHCP Snooping Commands User Manual for Network Management [65/79]

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User Manual

Chapter 5. Commands for DHCP Snooping 65

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resources of the switch, the actual number of trust users distributed depends on the

resource amount. If a bigger max number of users is set using this command, DHCP

Snooping will distribute the binding informaiton of untrust users to hardware to be

trust users as long as there is enough available resources. Otherwise, DHCP Snooping

will change the distributed binging informaiton accordint to the new smaller max user

number. When the number of distributed bingding informaiton entries reaches the max

limit, no new DHCP will be able to become trust user or to access other network

resouces via the switch.

 Examples: Enable DHCP Snooping binding user funtion on Port ethernet1/0/1, setting

the max number of user allowed to access by Port Ethernet1/0/1 as 5.

 Switch(Config-If-Ethernet1/0/1)# ip dhcp snooping binding user-control max-user 5

 Related Command: ip dhcp snooping binding user-control

5.16 ip dhcp snooping information enable

 Command: ip dhcp snooping information enable

 no ip dhcp snooping information enable

 Function: This command will enable option 82 function of DHCP Snooping on the

switch, the no operation of this command will disable that function.

 Parameters: None.

 Default Settings: Option 82 function is disabled in DHCP Snooping by default.

 Command Mode: Global Configuration Mode.

 Usage Guide: Only by implementing this command, can DHCP Snooping add standard

option 82 to DHCP request messages and forward the message. The format of option1

in option 82 (Circuit ID option) is standard vlan name plus physical port name, like

vlan1+ethernet1/0/12. That of option2 in option 82 (remote ID option) is CPU MAC of

the switch, like 00030f023301. If a DHCP request message with option 82 options is

received, DHCP Snooping will replace those options in the message with its own. If a

DHCP reply message with option 82 options is received, DHCP Snooping will dump

those options in the message and forward it.

 Examples: Enable option 82 function of DHCP Snooping on the switch.

 Switch(config)#ip dhcp snooping enable

 Switch(config)# ip dhcp snooping binding enable

 Switch(config)# ip dhcp snooping information enable

5.17 ip dhcp snooping information option allow-untrusted

 Command: ip dhcp snooping information option allow-untrusted

 no ip dhcp snooping information option allow-untrusted

 Function: This command is used to set that allow untrusted ports of DHCP snooping to

receive DHCP packets with option82 option. When disabling this command, all

untrusted ports will drop DHCP packets with option82 option.