| Description | This article describes how to troubleshoot the DHCP relay if the DHCP client cannot be assigned an IP address. |
| Scope | FortiGate. |
| Solution |
Topology:
Host(DHCP client)----(port2 10.57.1.147)FGT(port1 10.56.241.147)---------(10.56.241.172)DHCP Server
1) Make sure packet capture on port2 can receive DHCP requests from the client.
2) Run packet capture on the outgoing interface to verify if the DHCP request was sent through the DHCP server:
Note: It would be FortiGate's internal IP address 10.57.1.147 and NOT the external IP address 10.56.241.147 that sends DHCP Discover to the DHCP relay server. It would cause no reply if the DHCP server did not have the route to the 10.57.1.0/24 subnet.
3) Checking route back to 10.57.1.0/24 subnet on DHCP server: In this example, a static route is added to the DHCP server:
route add 10.57.1.0/24 MASK 255.255.255.0 10.56.241.147.
After that, FortiGate will receive a DHCP offer and ACK.
FortiGate then forwards ACK with the new IP address 10.57.1.2 to the Host.
Also, run dhcprelay debugs as mentioned below:
# diagnose debug application dhcprelay -1
Collect the reproduction logs, then disable debug:
# diagnose debug reset |
