changing a nic's mac address, freebsd6

David Kelly dkelly at
Wed Apr 19 14:46:52 UTC 2006

On Wed, Apr 19, 2006 at 08:33:53AM -0400, Dave wrote:
> Hello,
>    I've got an rl0 nic on a freebsd6 machine that i need to change it's mac 
> address on a tempoary basis. I will want to change it back when my testing 
> is complete. I read this was feasible with opbnbsd, and was wondering if 
> the capability was available in fbsd6? Also, does it matter which tempoary 
> mac address i give the card?

Presumably if one needed to change a MAC address one would already know
the MAC address one needed to change to. Otherwise make sure you are not
using an address currently in use on your network or the next router
over. Probably best to increment your current MAC by one.

Once Upon A Time I initialized a cable modem connection at a remote
office using my Mac PowerBook then replaced it with a FreeBSD machine
dedicated to serve as that office's router, firewall, and VPN gateway.
Rather than reinitialize the cable modem service with the FreeBSD
interface's MAC I left it using my PowerBook's MAC. The detriment was I
could no longer use my PowerBook in that office because it confused the
FreeBSD machine which saw another using its MAC address.

To set the MAC address before any other networking starts (such as DHCP)
create /etc/start_if.<interface name>

ifconfig <interface name> lladdr 00:11:22:33:44:55

If you make up an address the first octet probably should be 0 as there
are bits in that field which have special meaning.

David Kelly N4HHE, dkelly at
Whom computers would destroy, they must first drive mad.

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