Re: Loopback interface terminology issue

[神明達哉 <[e-mail]>]

At Mon, 16 Oct 2017 20:14:42 +0200,
Toerless Eckert <[e-mail]> wrote:

> > I don't understand what this means, but in any case I agree with Mark
> > that IMO this is more about the weak/strong host model than
> > forwarding/non-forwarding.
>
>                          ---etherB---
>       host --etherA-- rtr
>                          ---etherB---
>       |   host/rtr     |
>
> Think of a host with an etherA connecting to a router that also has
> etherB, etherC. Now we just integrate this router into the host and etherthernetA
> becomes an internal interface, but the apps can still use this interface,
> and so it is permissible for both strong and weak host models to use the IP
> address on etherA, whatever exernal ethernetB/ethernetC the packets are
> sent/received through.
>
> The main difference between an internal ethernet and loopback in this modelling
> is that when you send into a loopback interface, it does not need to run ND to
> find the link-local address of the router interface and forward the packet to it,
> but instead the packet is immediately processed by the router forwarding code.

Okay, I think I now understand what you meant.  Such a model seems to
be quite a stretch convoluted or even artificial to me, but I wouldn't
necessarily deny possible existence of such implementations.  But in
any event that seems to me quite a stretch from the situation Brian
originally raised.  And, for these reasons, I personally wouldn't
support saying something in the addressing architecture that requires
a specific model of integrated host-router architecture.  More
specifically I disagree with adding to the addrarch doc:

  If other addresses beside "loopback addresses" are assigned to such a link,
  then the interface needs to be configured to forward non-self-destined
  packets originated from the loopback interface (see rfc8200, section 2).

If it also notes that it's for a host that adopts the strong host
model or the node adopting the hybrid architecture you mentioned
above, I might live with it, although I personally think it's too much
for the basic architecture document.

--
JINMEI, Tatuya