Strange MAC address in my DHCP Server

[TT]

Hi all,

in my DHCP Server (the one embedded in windows 2000 server), I have
same strange MAC addresses in "Address Leases". These MAC addresses
have 40 hex digits instead of 12.
I could not find in all my network the PCs they belong.
What is it?
I'm afraid someone has gained access to the network via the WiFi area,
is it possible?
Or are there any network cards that do not work well?

Thanks to all.

 

[Steven L Umbach]

I am not that up to speed on the variances in mac address format but you may
also want to post in the server.networking newsgroup also. You can check for
computer names associated with those leases to see if that gives any clues.
If you have wireless and are using WEP [rather than WPA or 802.1X with
dynamic WEP] and have not changed the WEP key lately then maybe someone has
accessed your wireless network or if employees know the WEP/WPA key they
may be using their laptops on your network. There are network scanners that
you can use to scan your network to find the mac addresses and names of
active computers. If you are enforcing strong passwords on your network and
configure network resources with the principle of least privilege that can
mitigate the threat of unauthorized users from gaining access to your
network resources. --- Steve