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[ih] Origin of the loopback interface

there are two replies here, one to an echo through joe touch.

Toerless Eckert wrote:
> On Sun, Oct 22, 2017 at 03:19:50AM -0700, Paul Vixie wrote:
>> multihoming is one of the great unsolved problems in internetworking. we
>> do it properly on routers -- there, the loopback has the router's "real"
>> ip address -- but only because the router is on-path and can inject its
>> loopback address (which usually is not subnetted) into the topology.
> I am not sure if multihoming is a great unsolved problem in internetworking.
> It just seems to be a problem with IPs ideology. As opposed to let's say
> CLNS ideology of node addresses.
[description of how to have every endpoint participate in IGP]
> And thats just the tip of the iceberg.

since that was the straightforward way to do things when hosts got 
smarter and addresses were sprouting everywhere, i did it. the number of 
moving parts was high, and their state combinations and state transition 
ordering permutations were extreme, and debugging was hell, and i 
eventually had to say, it can't work with today's technology.

and that was before we learned about ARP spoofing. and before three 
decades of christmas tree packets and buffer overruns. so, i've revised 
my earlier "not with today's technology" assessment to "not ever."

i saw DEC AutoNet-II work at the Systems Research Center in 1990 or so 
and it was a thing of terrible power and beauty. i want a network that 
works like that. but, outside of the lab, and outside of hollywood, i 
aver that it cannot be done with multiple vendors, and should not be 
tried. forget about speed -- state is what kills.


Toerless Eckert wrote:
 > On Mon, Oct 23, 2017 at 12:42:29PM -0700, Joe Touch wrote:
 >> The problem with loop back is the assumption of locality, which is
 >> false without additional filters. Ipc typicallly defaults to local
 >> only until extended, which naps better to expectations.
 > I think there is only an assumption of locality on loopback
 > addresses, not interfaces. Which can be broken of course, but so can
 > locality expectations of other mechanisms. Unless one would even
 > start to define the exact behacvior of specific interfaces, yo could
 > never make an assumption of behavior using some type of interface
 > (across different implementations).

the internet is at its best an ad-hoc set of cooperative guidelines, and 
for all ad-hoc purposes for the last two decades, my template for every 
endpoint's host based firewall includes the following rules:

> add     pass    all     from any to any via lo0
> add     deny    all     from any to { ::1 or }
> add     deny    all     from { ::1 or } to any

i and many others have built mighty edifices upon the assumption of 
locality on the loopback interface. we merely ensure it as one of the 
requirements every endpoint must meet.


noting, elsewhere in this thread, someone said high performance like RVM 
API would be hard with IP even via a loopback. sun microsystems and cmu 
mach both had page flipping for page aligned data, largely because we 
all got tired of having to special case the local data path through 
"doors" or shared memory or "unix domain sockets". so, it can be hacked.

i think XNS was clearly superior to IP. but then, betamax was clearly 
superior to VHS, and look where that superiority got them. my short time 
programming device drivers for an AMD-based multibus board at ungermann 
bass to make sunos properly speak to XNS was maybe the most fun i'd ever 
had up until that day. but: the market has its own path.

P Vixie