Re: 127.0.0.1 deprecated??

[Dennis Ferguson <dennis.c.ferguson%gmail.com@localhost>]

On 20 Oct, 2014, at 17:32 , Robert Elz <kre%munnari.OZ.AU@localhost> wrote:
>    Date:        Mon, 20 Oct 2014 15:32:47 -0500
>    From:        Dennis Ferguson <dennis.c.ferguson%gmail.com@localhost>
>    Message-ID:  <E8CFDAF4-5E62-4EAD-9C99-919780DDE3C1%gmail.com@localhost>
> 
>  | 127.0.0.1 was just arbitrarily chosen for
>  | the 4.2 BSD lo(4) interface, there was no standard for that.
> 
> Dennis, do you know/remember whether Berkeley actually invented that
> use, or did they "borrow" it from elsewhere?   I never knew (and don't
> think I ever bothered to ask), it just seemed to be there from the very
> first time I saw the networking code.

I'm not sure.  The only other networking I saw that early was the BBN
stack that was used with 4.1 BSD sometimes, and I wasn't familiar with
it since the kernel sources weren't on the machine I had access to,
but I recall that machine having a loopback interface that was left
unconfigured.  I think that wasn't a possibility for 4.2 BSD, in fact
I think the 127.0.0.1 was hardwired so that if networking was configured
in the kernel it booted with lo0 already configured with the address.  You
could change the address but I'm not sure you could delete it.  There
was something about the 4.2 code that really, really wanted at least
one fully configured interface at all times, so I think the hardwired
loopback address might have been a hack-around for that (this also might
be why the machines were so prone to getting attached to that address
early and then sending packets sourced from it out the real network
interface later).

I hence wouldn't be surprised if Berkeley actually invented it, since
they were the ones with a need for a hardwirable address like that.
And the timing is right; you would never pick network 127 for this prior
to network classes, and classed networks officially arrived not too
long before the first Berkeley networking did.

Note that I only remember (or maybe misremember) any of this because
4.2 BSD was the first operating system I ever saw with a network stack,
and I was fascinated enough by it that I spent quite some time figuring
out how that code worked.  In retrospect it probably wasn't the most
wonderful example of that art, but at the time I thought it was
absolutely excellent.

Dennis Ferguson