[e2e] use of MAC addresses

Joe Touch touch at ISI.EDU
Wed Apr 12 08:50:53 PDT 2006

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. 

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.


 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?

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