[DHCP issue] The interface vlan 1 can't get the IP address via DHCP relay on the L3 switch

Topology:

The connection between the L3 switch and vDHCP is over layer 3.

The interface vlan 1 of spine and leaf can"t get the IP address from the DHCP relay on the L3 switch.

Step 1. Checking the DHCP relay configuration on the L3 switch.

interface Vlan-interface1

ip address 120.x.x.1 255.255.255.0

dhcp select relay

dhcp relay server-address 110.x.x.105

dhcp relay server-address 110.x.x.106

The configuration is correct.

Step 2. Make sure the interface vlan 1 of spine and leaf is in the same layer 2 domain with the interface vlan 1 of L3 switch.

One can set a static IP address on the interface of spine or leaf and ping to the interface vlan 1 of L3 switch. Check the connectivity.

Step 3. Check the routing table of DHCP server on the L3 switch, make sure there are routes to the DHCP server.

ping -a 120.x.x.1 110.x.x.105 is passed.

After all above checking steps, all checking are passed, while the spine and leaf can get the IP address for vlan 1. According to the packets capture, the DHCP relay packets are sending with the source IP 6.6.6.6 which is the IP address of the routing outbound interface, and there is no routes in the network to send the packets back to 6.6.6.6. So the DHCP server can"t replay the DHCP relay packets.

Adding configuration as following:

#

interface Vlan-interface1

ip address 120.x.x.1 255.255.255.0

dhcp select relay

dhcp relay server-address 110.x.x.105

dhcp relay server-address 110.x.x.106

dhcp relay source-address 120.x.x.1

#

Then issue solved.