Fake eth0

[Bob Chiodini]

On Fri, 2006-02-17 at 12:11 -0500, Gene Heskett wrote:
> On Friday 17 February 2006 03:37, Nguyen Danh Hieu wrote:
> >Hi everybody.
> >Sorry for my poor English but I have a trouble with ethernet
> > interface. I have a new LAN-card on  my machine but MAC-addresss of
> > old card is registered so I have to fake MAC address of the new to be
> > able to use LAN. I do it with command:
> >/sbin/ifconfig eth0 down
> >/sbin/ifconfig eth0 hw ether xxxxxxxxxxxxx
> >/sbin/ifconfig eth0 up
> >
> >and MAC is faked, but after that card seem to not work.  no packages
> > are send and received.  When I restart computer Lan-card work again
> > but with his own MAC so is not registered.
> >
> >Please help me out of the  problem.
> >Thank you.
> 
> I believe this is an arp problem.  One might have to go around to all 
> the other boxes on your network that keep track of such things, and all 
> of them should, and find and delete the entries in each of the other 
> machines arp tables so that the new MAC address can be inserted without 
> the address clash its creating now.
> 
> And thats as close to telling you how that I can do because its been >1 
> years since I had to do that here at home and I didn't make a consious 
> effort to commit the exact details of it to long term memory in my 
> ancient wet ram here.
> 
> Another possibility might be to give this newer card a different ip 
> address, but that would require updateing the hosts files across your 
> network too.  I'd prefer not to have to do that myself.
> 
> >

I think the ARP caches will eventually expire.  It might be minutes.

A possible problem would come if the NIC sends anything prior to
initialization with the new MAC.  The upstream switch may cache the
first MAC it hears and disallow differing MACs arriving at the NIC's
port.  Cisco switches have the capability to do this.  What does arp -a
tell you when run on another box on the same LAN?

With the suggested modifications to the ifcfg-eth0, what does ifconfig
tell you after bootup?

Can't the network admin re-register your new NIC?

Bob...