13.2.2 Basic Settings
This subsection describes the basic configuration for using DHCP snooping.
The following figure shows an example of a basic configuration for DHCP snooping.
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![[Figure Data]](./GRAPHICS/ZU216100.GIF)
- <Structure of this section>
(1) Enable DHCP snooping
- Points to note
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Enable DHCP snooping on the entire switch and specifies the VLAN where DHCP snooping needs to be enabled.
Command examples
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(config)# ip dhcp snooping
Enables DHCP snooping on the entire switch.
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(config)# vlan 2
(config-vlan)# exit
(config)# ip dhcp snooping vlan 2
Enables DHCP snooping on VLAN ID 2. DHCP snooping is enabled only on the VLANs that are specified by using this command.
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(config)# interface gigabitethernet 1/0/1
(config-if)# switchport mode access
(config-if)# switchport access vlan 2
(config-if)# exit
Sets port 1/0/1 as an access port, and sets VLAN ID 2 as the VLAN containing port 1/0/1.
(2) Configuring DHCP snooping's trust
- Points to note
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Set the port that connects to DHCP server (in "Basic Configuration of 13-10 DHCP snooping Diagram", the port that connects to the Layer 3 Switch/router) as trust port.
Command examples
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(config)# interface gigabitethernet 1/0/5
(config-if)# ip dhcp snooping trust
(config-if)# switchport mode access
(config-if)# switchport access vlan 2
(config-if)# exit
Sets port 1/0/5 as a trusted port. Other ports are untrusted. The sequence also sets port 1/0/5 as an access port and sets VLAN ID 2 as the VLAN containing port 1/0/5.
(3) Setting the Binding Database Destination
(a) To save data to the internal flash memory
- Points to note
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Set internal flash memory as the location for saving the binding database.
Command examples
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(config)# ip dhcp snooping database url flash
Sets internal flash memory as the save location.
(b) To save to MC
- Points to note
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Set an external memory card as the location for saving a binding database. If you set an external memory card, you can specify the name of the file for saving the database.
Command examples
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(config)# ip dhcp snooping database url mc dhcpsn-db
Sets an external memory card as the save location and sets dhcpsn-db as the name of the file for saving the binding database.
- Notes
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Before you set an external memory card as the save location, make sure a card is already inserted in the memory card slot on the Switch. In addition, use memory cards manufactured by ALAXALA.
(4) Setting the Write Latency to the Binding Database Destination
- Points to note
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Set a delay time to be applied before a binding database is saved.
Command examples
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(config)# ip dhcp snooping database write-delay 3600
Sets 3600 seconds as the length of time to wait after one of the following save events occurs before saving actually starts:
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When terminal information is dynamically registered, updated, or deleted in the binding database
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When the ip dhcp snooping database url configuration command is specified (includes a change of save location)
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When the clear ip dhcp snooping binding operation command is executed
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- Notes
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The length of time set by this command becomes operationally effective from the next save event.