there is a network configured in Mikrotik and configured a DHCP relay for that network. The DHCP server is a openwrt dnsmasq.
The problem is very trivial and simple to reproduce:
1. DHCP leased an IP address to a client in that network successfully. It is a static leased IP address which means that the MAC address is bounded to that specific address and each time the client always get the same IP address.
2. I changed the IP address assignment of that client in the DHCP configuration.
3. I force the client to renew its IP address before it is expired. In general, the client send a request to extend the leasing time to its original IP address.
4. The DHCP server response with a NAK "address not available" (because the original address is not bounded to it anymore). Mikrotik also received this DHCP response (confirmed with package capture)
5. The DHCP relay DOESN'T forward that NAK to the client. ( I can verify it with the counter of "request" and "response" at the DHCP relay webgui, the "request" keep increasing but no count on "response" )
6. The client cannot get the new address and remains to the old address as it don't have any response from the DHCP server.
I believe there is a bug in the DHCP relay in mikrotik that it doesn't implement the forwarding of DHCP NAK to the client. This is a huge drawback in IP address management aspect as the change of the IP address need to be wait until the target IP address expires.
The problem is very trivial and simple to reproduce:
1. DHCP leased an IP address to a client in that network successfully. It is a static leased IP address which means that the MAC address is bounded to that specific address and each time the client always get the same IP address.
2. I changed the IP address assignment of that client in the DHCP configuration.
3. I force the client to renew its IP address before it is expired. In general, the client send a request to extend the leasing time to its original IP address.
4. The DHCP server response with a NAK "address not available" (because the original address is not bounded to it anymore). Mikrotik also received this DHCP response (confirmed with package capture)
5. The DHCP relay DOESN'T forward that NAK to the client. ( I can verify it with the counter of "request" and "response" at the DHCP relay webgui, the "request" keep increasing but no count on "response" )
6. The client cannot get the new address and remains to the old address as it don't have any response from the DHCP server.
I believe there is a bug in the DHCP relay in mikrotik that it doesn't implement the forwarding of DHCP NAK to the client. This is a huge drawback in IP address management aspect as the change of the IP address need to be wait until the target IP address expires.
Statistics: Posted by tawhwat — Tue Jun 10, 2025 10:36 pm