[e2e] use of MAC addresses

Joe Touch touch at ISI.EDU
Thu Apr 13 14:29:07 PDT 2006

Charles M. Hannum wrote:
> I'm still trying to figure out where this notion of IP addresses being
> "globally unique" came from.  IP addresses are *not* globally unique.

RFC1122, pg. 18. There are exceptions where a number of interfaces are
working together, whether on a single host or multiples, as a single
virtual device, but that's a very subtle issue by comparison.

> Even if we ignore NAT, they are still ephemeral due to DHCP, ND, etc.

Ephemeral doesn't mean that at a given time only one host (or virtual
host) should be using a single IP address.

> The big selling point of MAC addresses is to make it easy to implement
> determistic algorithms for discovering and maintaining IP address
> mappings. 

That's only relevant for shared media. Point-to-point media don't need
that capability.


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