Re: Loopback interface terminology issue

[Karl Auer <[e-mail]>]

On Sat, 2017-10-14 at 14:11 +1300, Brian E Carpenter wrote:
> (RFC 4291, section 2.5.3). The text only mentions the loopback
> address ::1.

Need to stay clear on the difference between a loopback interface and
the concept of localhost.

::1 is the localhost address; use it, and you are talking to "this host
right here". It doesn't have to be on a loopback interface, but it
generally makes sense for it to be, because a device may have no real
network interfaces at all, but you still want to be able to talk to
services running on it.

And similarly, loopback interfaces do not necessarily have to have a
localhost address on them. You can have lots of loopback interfaces on
a host, and they present variations of "this host right here" e.g. by
participating in different routing schemes or having particular
services on them. The interface is not the canonical identity of the
host, the localhost address is. That is ::1 in IPv6.

Things have become confused over the years because of the very strong
convention that "the" localhost address is on a loopback interface.

The fact that there is only one (1) localhost address in IPv6 vs the
entire /8 reserved in IPv4 is, I always thought, specifically to make
the distinction clear.

Or maybe it's just me.

Regards, K.

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Karl Auer ([e-mail])
http://www.biplane.com.au/kauer
http://twitter.com/kauer389

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