Re: Network Probs (was Re: Firewall issues)

From: "Rick Warner" <[email protected]>

> On Wed, 11 Jun 2003, jdow wrote:
>
> > Two cards with the same MAC address is deadly. How many other such
> > situations exist on the network? This condition will lead to misdirected
> > and lost packets. So if there is a way to change the MAC address of
> > those cards do so.
> > {^_^}
> >
>
> Whoa..... no need to light the fires of fear yet.  You can have dozens
> of network cards with the same MAC address *as long as they are on
> separate networks*.   Let me rephrase that; the only time you cannot have
> two cards with the same MAC address is if they are on the same network.
> MAC address are only visible on the local network; once a packet traverses
> a router, the next device downstream sees the MAC address of the router
> as the source, and so on.  Sun machines use a MAC address in the PROM
> for all network interfaces; I have worked with Sun boxes with up to
> 16 network interfaces all with the same MAC address.   No problem as each
> interface was on a different network.
>
> - rick warner

That doesn't upset the ARP configuration? I had this situation under
5.1 and it just plain did not work at all. Fortunately my eye caught
the MAC address duplication on two cards and I gave up attempting two
networks off that machine. I developed an adequate workaround for the
then rather modest network needs. (I'd wanted a separate network at
10.x.x.x for testing a specific "gadget" we had.) I've wondered if this
is where some of the superstition about not having two cards from the
same vendor or with the same chip in the same machine came from. It
certainly worked OK on a later machine with two RealTek based cards
from different vendors and now with two from the same vendor. The MAC
addresses are different, though.

{^_^}