I set up a small Windows 10 Pro system running Tiny PXE to provide DHCP and PXE services on a dedicated 192.168.26.x network for installing and testing servers and network equipment. The company's normal network uses 192.168.1.x and a DrayTek Vigor router, where this problem does not occur.
The issue appears when I connect cables to dedicated BMC management ports, including Dell iDRAC, HPE iLO, and Lenovo XCC interfaces. Tiny PXE logs show different MAC addresses requesting leases, but the server sometimes assigns the same IP address to more than one device.
I retested this with three Dell servers:
- T160-1: c4:d6:d3:5a:fd:4c
- T160-1: c4:d6:d3:5c:24:30
- R360: 84:5c:31:b0:1d:f6
A Wireshark capture showed Tiny PXE assigning 192.168.26.200 to two different machines, even though they had different MAC addresses and client IDs. The BMC interfaces are configured to use their dedicated ports rather than shared network ports. What could cause this, and how can I prevent duplicate DHCP leases?
3 Answers
The usual cause is that a BMC is configured for shared or failover networking and is sending DHCP requests through more than one interface. Even if the cable is connected to the dedicated port, check each server’s management-network setting in the BIOS or BMC configuration and explicitly select the dedicated interface. Also verify that the Ethernet switch is not bridging or incorrectly forwarding those ports.
Check whether the BMCs are sending BOOTP-style requests or unusual DHCP options, and confirm that the test switch is passing broadcasts normally. For a stable management network, assigning static BMC addresses or creating reservations based on each BMC’s MAC address is also a good workaround. Keep those addresses outside the dynamic pool so the DHCP service cannot hand them to another device.
This may be a limitation or bug in Tiny PXE’s DHCP implementation rather than a problem with the BMCs. Compare the complete DHCP exchange for both clients, including the DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, and DHCPACK packets. Check whether the server is reusing an address because of an incorrect lease table, a duplicated client identifier, or a pool-management problem. Testing the same isolated network with another DHCP server would quickly help separate a client issue from a Tiny PXE issue.
The interfaces were reported as dedicated, so shared-port behavior is less likely here. Since the packets show different MAC addresses and client IDs, the DHCP server should still be treating them as separate clients; the lease-allocation behavior of Tiny PXE needs closer investigation.