weird MAC address in DHCP binding

[treska-eu]

Hi, i have problem whith Cisco DHCP. On switch C6506 in "sh ip dhcp binding" table are the weird MAC address. What is the problem? The one MAC have more IP address:

158.195.40.46   id    ffe6.448a.e400.0100.011d.69e6.3900.16e6.448a.e4  Mar 12 2016 03:35 PM

158.195.46.201  id    ffe6.448a.e400.0100.011d.d88f.c400.16e6.448a.e4  Mar 12 2016 12:10 PM

158.195.46.202  id    0100.16e6.448a.e4  Mar 12 2016 02:09 PM

158.195.46.203  id    ffe6.448a.e400.0100.011d.d8b0.1b00.16e6.448a.e4  Mar 12 2016 02:28 PM

158.195.46.204  id    ffe6.448a.e400.0100.011d.d8b2.0500.16e6.448a.e4  Mar 14 2016 09:53 PM

[Peter Paluch]

Hi,

It seems that the client is, for some reason, using RFC 4361-compatible IDs. These consist of two parts: First, the so-called IAID (Identity Association ID) that uniquely identifies the client's interface (4 bytes); second, the so-called DUID (DHCP Unique ID) that identifies the entire client as an entity.

It would appear that the IAID that keeps repeating is e6-44-8a-e4, and the DUID that always begins with 00.0100.011d... is using the format based on the local MAC address and the time - this is given by the two leading octets of the DUID which is 0001.

It thus appears that this is a client whose DHCP client is configured to use RFC 4361-compatible IDs but that does not permanently store its generated DUID, and always generates it anew based on the current time. That would explain its tendency to request multiple leases from the DHCP server, always getting a new one.

What is the operating system running on that host?

Best regards,
Peter

[treska-eu]

OS is Fedora

Michal

[Peter Paluch · Accepted solution]

Hi Michal,

Okay. Please check the file /etc/dhcp/dhclient.conf on the Fedora machine and add the following line to the file:

send dhcp-client-identifier = hardware;

If there are any other instances of this command in that file, please remove them - make sure this is the only one.

Best regards,
Peter

[hoylea]

you can also use :  address 10.100.100.100 client-id ffe6.448a.e400.0100.011d.d8b0.1b00.16e6.448a.e4