I have two VLANs, 10 and 40, with external ISC-DHCP servers in VLAN 10. I am successfully relaying DHCP across VLANs: a PC in VLAN 40 can request a DHCP lease, receive the offer, and accept the IP. My working configuration includes:
ip dhcp relay address 10.10.0.17
ip dhcp relay address 10.10.0.18
ip dhcp relay enable
!
interface vlan 10
name Engineering
ip address 10.10.0.6 255.255.255.0
ip dhcp relay enable
!
interface vlan 40
name Family
ip address 10.40.0.6 255.255.255.0
ip dhcp relay enable
!
To enable IP DHCP snooping, I did the following:
interface GigabitEthernet24
ip dhcp snooping trust
!
interface GigabitEthernet25
ip dhcp snooping trust
!
ip dhcp snooping
ip dhcp snooping vlan 10
ip dhcp snooping vlan 40
Where the two DHCP servers are on gi24 and gi25. As soon as this configuration is applied, the same PC in VLAN 40 can no longer receive a DHCP lease. On the ISC-DHCP server I see:
2024-10-14T12:52:31.680159-06:00 pi00 dhcpd[171061]: DHCPDISCOVER from d4:5d:64:b5:bb:e7 via 10.40.0.6
2024-10-14T12:52:31.681405-06:00 pi00 dhcpd[171061]: DHCPOFFER on 10.40.0.13 to d4:5d:64:b5:bb:e7 via 10.40.0.6
2024-10-14T12:52:47.160553-06:00 pi00 dhcpd[171061]: DHCPDISCOVER from d4:5d:64:b5:bb:e7 via 10.40.0.6
2024-10-14T12:52:47.161200-06:00 pi00 dhcpd[171061]: DHCPOFFER on 10.40.0.13 to d4:5d:64:b5:bb:e7 via 10.40.0.6
To get the PC talking to my DHCP servers again, I issue:
no ip dhcp snooping
Then the PC almost immediately receives the DHCPOFFER and responds with DHCPREQUEST.
What configuration am I missing that would enable DHCP relay and DHCP snooping?
