[e2e] use of MAC addresses

Fahad Dogar fahad.dogar at gmail.com
Wed Apr 12 10:02:33 PDT 2006

I understand why IP addresses (which are hierarchical in nature) are
needed but can't seem to appreciate the use of MAC addresses, in
addition to using IP addresses. Practically I can understand that they
are being used for legacy purposes and a move towards using IP
addresses as layer 2 addresses would require changes in ethernet
switches etc. But I am interested in knowing whether, in theory, we
would be restricted in functionality if we use IP addresses for layer
2 addressing. Suppose we were to redesign layer 2 technologies now,
can we use IP addresses in place of MAC addresses. With IPv6 I can't
even see any constraint on the address space.


On 4/12/06, Joe Touch <touch at isi.edu> wrote:
> Ted Faber wrote:
> > On Tue, Apr 11, 2006 at 12:20:47AM +0500, Fahad Dogar wrote:
> >> Hi all,
> >>
> >> I have a very basic question: in theory, can we NOW use IP addresses
> >> in place of MAC addresses.
> >
> > Short answer: "yes," with an "if."
> > Long answer: "no," with a "but."
> >
> > IP addresses are (in principle) globally routable.
>                                 ^
>                              easily
> You can route on MAC addresses too, but being flat that means core
> routing tables would need to be flooded with everyone's MAC address.
> Look at the size of your routing table. Then look at the size of your
> ARP table. If your routing table has anything except default addresses,
> consider that ARP table size multipled by the size of the number of
> subnets at each other route entry.
> Joe
>  Having a locally
> > routable namespace under your link layer's complete control may be a
> > useful thing.
> >
> > It's rare in the world of computers that removing a layer of indirection
> > makes your system more versatile.  There are quite a few tricks that
> > take advantage of the layer of indirection that a link layer address
> > provides to give faster response on a subnet basis, simple redundancy,
> > etc.
> >
> > Of course you could get rid of them (assuming you're willing to live in
> > the smaller, more constained IP address space).  An identifier's an
> > identifier.
> >
> > Why would you want to?
> >

More information about the end2end-interest mailing list