Windows Server - DHCP IP Reservations issue - Page 1
Forum section: electronics / general

author: IanJ
author_rank: Unknown
timestamp: November 20, 2023, 10:26:30 am
content: Wierd issue (for me!) in relation to my newly set up Windows Server DHCP IP reservations.Basically, I am binding MAC addresses to IP's for the devices I cannot set a fixed IP on.One such device is my Bosch Solar Inverter.Logging into the Bosch unit the MAC address is displayed in the config - CHECKRunning CMD linearp -a 192.168.1.138I get the same MAC address - CHECKHowever, Windows Server DHCP reservation doesn't work, the Bosch always picks up a new dynamic IP address instead of the reserved one......!So, instead of setting up a manual reservation I let it get a new dynamic IP address and right clicked the new lease and chose 'Add To Reservation'.Viewing the MAC address there is some32 characterhex string instead of the usual shorter format.From there though the reservation with that MAC address works perfectly, and so I asked Chat GPT what was this all about:ChatGPT:The address seems to be a hexadecimal representation of ASCII charactersSo, for example the first two numbers of the MAC address it should be "00:60......"But the string shows "302d3630......"30 = 02d = -36 = 630 = 0It looks like the MAC address of the Bosch inverter is being reported in an unusual way.Wierd, but at least it now works. Just wondered if this is really an unusual issue or if it's quite common etc.Ian.

author: eutectique
author_rank: Frequent Contributor
timestamp: November 20, 2023, 04:57:46 pm
content: What doesipconfigreport back?Edit:ipconfig /allis even better.

author: jc101
author_rank: Frequent Contributor
timestamp: November 20, 2023, 07:02:43 pm
content: That sounds like an IPv6 address, which is 32 hex digits long.Do you have IPv6 enabled on any of the boxes?

author: IanJ
author_rank: Unknown
timestamp: November 20, 2023, 07:51:59 pm
content: Quote from: jc101 on November 20, 2023, 07:02:43 pmHere my number, data removed (# representing 1 hex digit) but leaving the "2d" hex dashes which ChatGPT pointed out to me:##2d####2d####2d####2d####2d####0r,##-####-####-####-####-####IPV6 is colons, and would be:####:####:####:####:####:####:####:####If it's a DHCPv6 Client DUID then it would be:##-##-##-##-##-##-##-##-##-##-##-##-##-##The actual Bosch Inverter has a web login, and in there it lists only an IPV4 MAC address.Ian.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: November 20, 2023, 08:07:57 pm
content: Might be a DHCP conflict? Check the server subnet is something like 255.255.255.0, the inverter is expecting to be a DHCP client and, the port is plugged on a phy-interface matching the 192.168.1.* subnet.As suggested, run ipconfig /all at the comand prompt

author: IanJ
author_rank: Unknown
timestamp: November 21, 2023, 10:04:09 am
content: IPConfig/all findings:-From the PC I run it on (My Dev PC) it has a fixed IP, and it's set to the same IP that the DHCP server would have given it via it's MAC. The DHCP server confirms it has allocated it (inactive).I would note that the DNS I have manually set on the DevPC isn't the same as configured on the DHCP server. I doubt this would cause an issue from my knowledge.Subnet Mask, Gateway etc all ok.Two other network adaptors in the DevPC are currently inactive/disconnected (VPN & Bluetooth).I guess then I'll just leave this as a Bosch Inverter anomoly where it's misreporting it's MAC address but that Windows DHCP Server is able to pick this up and work around it successfully thanks to ADD TO RESERVATION option from the dynamic pool. Without that it would have been just about impossible.Ian.

author: Halcyon
author_rank: Unknown
timestamp: December 04, 2023, 11:17:37 am
content: I have a Bosch inverter and have had no troubles with DHCP, that being said, I use pfSense, not Windows.You may have to do a packet capture and see what the DHCPDISCOVER/OFFER/REQUEST/ACK messages actually are. What you may be seeing with that "shortened" MAC is the actual address but in hexadecimal format (that's what would be passed in the packet).

author: PlainName
author_rank: Super Contributor
timestamp: December 04, 2023, 04:01:27 pm
content: Perhaps use Wireshark (or equivalent) to see what's going over the wire. My DHCP server (Windows-based but deffo not Microsoft) reports two different formats for MAC address: with and without colons. I doubt if the server is randomly picking how to format them but is showing the raw data as it's received, so it could be that what goes over the wire isn't necessarily what you see when the device, or PC, pretty-prints them for display.

author: Ranayna
author_rank: Super Contributor
timestamp: January 08, 2024, 09:11:42 pm
content: I have seen longer IDs on Windows DHCP for Raspberry Pis in the past.https://forums.raspberrypi.com/viewtopic.php?f=28&t=110331Maybe the issue is related? Who knows what operating system that iverter is running, maybe it even contains a Raspberry Pi?