10-23-2009 07:17 AM - edited 03-06-2019 08:16 AM
Hi to All,
I have multiple VLANs configured on a L2/L3 switch (cisco 3750) and one DHCP server configured on wan [using ip helper-address on the switch I forward the DHCP request on a L3 interface (the port vs the DHCP server is a routed port)].
If I enable dhcp snooping on the switch I need also to configure the TRUSTED PORT (the port vs the DHCP server) but I cannot configure it as it's a L3 routed port vs the wan router.
How it's possible to enable DHCP snooping on the switch and use the DHCP server on the "wan" ?
Regards
Solved! Go to Solution.
10-24-2009 04:07 AM
Hello Roberto,
I was thinking of:
ip dhcp snooping
! enables for all vlans
no ip dhcp snooping vlan 3
! disabling DHCP snooping for core facing
! vlan
but your configuration should be fine, only doubt is that a general
ip dhcp snooping
may be needed
Hope to help
Giuseppe
10-23-2009 11:33 AM
Hello Roberto,
a routed port is not part of any Vlan so DHCP snooping is not running on it.
if you use an SVI + a physical port as your core facing link you can still disable ip igmp snooping on the associated L2 vlan.
Hope to help
Giuseppe
10-23-2009 12:00 PM
Hi Giuseppe,
thanks for the info.
Please can you check the conf. and tell me if will be correct ?:
THE CURRENT SWITCH CONFIGURATION
!
!
interface GigabitEthernet1/0/1
description ** DHCP pc 192.168.2.0/24 **
switchport access vlan 2
switchport mode access
load-interval 30
!
interface GigabitEthernet1/0/2
description ** DHCP pc 192.168.2.0/24 **
switchport access vlan 2
switchport mode access
load-interval 30
!
interface GigabitEthernet1/0/3
description ** DHCP pc 192.168.2.0/24 **
switchport access vlan 2
switchport mode access
load-interval 30
!
interface GigabitEthernet1/0/24
description ** TO WAN ROUTER **
no switchport
ip address 192.168.254.254 255.255.255.252
!
interface Vlan2
description ** LAN **
ip address 192.168.2.254 255.255.255.0
ip helper-address 192.168.1.254
!
ip forward-protocol udp bootpc
!
ip route 192.168.1.0 255.255.255.0 192.168.254.253
!
THE NEW SWITCH CONFIGURATION
!
ip dhcp snooping Vlan 2
!
interface Vlan3
description ** LAN TO WAN ROUTER **
ip address 192.168.254.254 255.255.255.0
!
interface GigabitEthernet1/0/24
description ** TO WAN ROUTER **
switchport
switchport access Vlan 3
ip dhcp snooping trust
!
Regards
Roberto Taccon
10-24-2009 04:07 AM
Hello Roberto,
I was thinking of:
ip dhcp snooping
! enables for all vlans
no ip dhcp snooping vlan 3
! disabling DHCP snooping for core facing
! vlan
but your configuration should be fine, only doubt is that a general
ip dhcp snooping
may be needed
Hope to help
Giuseppe
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