MAC-address Vendor

[Wolfgang Orth]

Hello all,

in my SOAP-Server I store the Computername and the MAC-Address for some significant reason (explanation below). Now I noticed, that one computername is listed twice in my database, with two different MAC-Addresses. One MAC-Address is apparently from an Intel-NIC. The other, differening only in the first and the last byte, is completely unknown, seems to have no vendor. *)

I also see, that this desktop-name is used from the same public IP-Address. That lets me assume to be the the identical computer. But how can it be, that this PC has a valid MAC-Address on one day, a different, "invalid" one the next day?

Does anyone know more about this? Could it be a virtual machine with revolving MACs?

The significant reason explained: This SOAP-Client-Server-combo is meant to be used inside a LAN. On first contact between client and server, the computername and its MAC-Address get joined with the department the user selects from a list, then gets stored in the DB. Now we can make a machine log-in, we can avoid a user log-in. Its meant for convenience. Computername + MAC-Address have to be unique.
I know these data, because they appeared in the DB of my publicly available demo. However, its an anonymous demo, there is no chance to get a hold on that person and ask directly.
The ISP-issued IP-address, from where the computer got connected to my server, was the same over several days, albeit the number seems to not come from a pool of static addresses. Normally ISP's disconnect every 24 hours, so every day a normal, private customer gets a new one. Which private user runs virtual machines? But it is also not recognizable, whether the IP-Address is issued to a company. It seems to be a pool of dynamic addresses. And corporations have their own address-blocks.

Thank you for your patience - and for any input!
Wolfgang


*) The IEEE issues a  24 Bit identifier to vendors, the Organizationally Unique Identifier (OUI). The vendors normally use this as the first three bytes in the MAC-Address.
https://standards.ieee.org/products-services/regauth/oui/index.html

[Bruce]

Hi Wolfgang,

>> I store the Computername and the MAC-Address

There is no such thing as "the" MAC address. MAC addresses belong to the Network interface, not the machine. So a machine with multiple network interfaces will have multiple MAC addresses. For example a laptop with both a wifi and ethernet port will have 2 MAC addresses.

You can see this in NetDemo, Extra menu, IP List. Multiple interfaces, multiple MAC addresses. That makes use of this function;
https://www.capesoft.com/docs/NetTalk11/NetTalkUtilityFunctions.htm#NetGetIPInfo

The root of the problem though is this;

>> Computername + MAC-Address have to be unique.

Actually they are not always unique (MAC addresses can be spoofed.) - But even if they are unique they are not "alone". In other words you can have multiple values for the same machine.

Cheers
Bruce