[e2e] use of MAC addresses

[Charles M. Hannum]

On Tue, Apr 11, 2006 at 12:20:47AM +0500, Fahad Dogar wrote:
> I have a very basic question: in theory, can we NOW use IP addresses
> in place of MAC addresses. In other words, is there any other use of
> MAC addresses other than using them for legacy reasons?

I think this depends a little on whether you're talking strictly about
the host side, or if you're including networking equipment.  MAC
addresses are used in spanning tree, for example, which is pretty
fundamental to modern Ethernet switching.  They're also heavily used in
802.11.

Also, there are some advantages to having a globally unique identifier:

* The separation is used to detect IP address duplication.

* MAC address filtering is used by some whizzy hotel connectivity
solutions that don't require users to reconfigure their laptops (even
though they may have conflicting IP addresses).

* An interface may have many IP addresses (I've considered allowing
mask-based addresses in NetBSD; i.e. configure an interface to respond
to 128.52.26/24), but only one MAC address, which simplifies the
address filtering on the NIC.  (This is not so important with P2P
links, and you'll notice that many P2P protocols don't have link-level
addresses.)

So, the short answer is that you *could* eliminate MAC addresses, but
it would involve changing several well-established protocols, and you'd
potentially lose some functionality.  So why bother?