[e2e] What should e2e protocols know about lower layers?

[Erik Nordmark]

Joe,

> IPv4 certainly has a notion of local - the subnets to which you are 
> directly connected. This is why, IMO, broadcasts are permitted there.

If IPv4 has such a notion from a congestion control
perspective then something is broken.
RFC 2002 (Mobile IP) uses IPinIP tunneling to make what you thought was 
local (in the same subnet prefix) be capable of being anywhere in the Internet.
 The only notion of "local" I've seen in IETF standards for IP
is whether to ARP (or similar mechanisms for link-layers that don't
use ARP) or send to a router. But that notion doesn't imply anything other
that direct L2 reachability., which in turn doesn't imply anything about
the performance and congestion sensitivity characteristics
of that L2 (and whether those characteristics are uniform across
all destinations on that L2).

    Erik