IP DHCP snooping

[getaway51]

Hi,

May I know what this command will do to DHCP messages? I mean will it block or allow DHCP request and reply to connected stations?

ip dhcp snooping vlan 30
no ip dhcp snooping information option
ip dhcp snooping

[luis_cordova]

Hi @getaway51,

I think this links can help you:

http://www.pearsonitcertification.com/articles/article.aspx?p=2474170

https://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/n5k/commands/ip-dhcp-snooping-information-option.html

Regards

[getaway51]

May I ask if i enable I have configure ip dhcp snooping & ip dhcp snooping vlan, all ports will be disable for sending out DHCP reply, right? 

Unless I have configure on tht interface "ip dhcp snooping trust"?

[Seb Rupik]

Hi there,

Yes, configuring 

!
ip dhcp snooping
ip dhcp snooping vlan xxx
!

Will drop all DHCP replies on untrusted ports. To permit the replies you need to add:

!
ip dhcp snooping trust
!

...on the switchports leading towards the DHCP server.

cheers,

Seb.

[getaway51]

Hi,

I need to configure this (ip dhcp snooping trust) on ALL the Uplink or Trunk ports? 

[Seb Rupik]

Yes, however you typically only want DHCP snooping to be enabled on the access-layer. You should not be configuring it on the distribution or core layers.

Unless the DHCP server is connected to the access switch (in which case make that switchport trusted), so should want to configure the ip dhcp snooping trust  on the uplinks.

cheers,

Seb.