[systemd-devel] nss-myhostname: why don't loopback interfaces appear?

[Lennart Poettering]

On Wed, 03.06.15 16:31, Daurnimator (quae at daurnimator.com) wrote:

> On 3 June 2015 at 16:01, Lennart Poettering <lennart at poettering.net> wrote:
> > On Wed, 03.06.15 15:40, Daurnimator (quae at daurnimator.com) wrote:
> >
> >> I was playing around with nss, and found that my loopback interface ip
> >> doesn't appear from nss-myhostname.
> >> Rather, my other ones do.
> >> Furthermore, unless I request IPv4, link-local IPv6 addresses are
> >> returned. Is this expected?
> >
> > We order the returned addresses by scope. Global addresses are
> > placed first, local ones last.
> 
> Then why are link local IPv6 addresses returned first?
> 
> If this was the case, I would expect to see:
> 
> 192.168.2.229
> 192.168.2.21
> fe80::aed1:b8ff:fec0:d113
> fe80::9eeb:e8ff:fe1b:f42d
> 127.0.0.1
> ::1

Currently the first ordering key is the address family (ipv4 before
ipv6), the second ordering key is the scope (global before
link-local). 

Are you suggesting we should turn this around, and sort by scope
first, and by address family then? I might be open to such a change.

> > We return addresses on the loopback device only when there's no other
> > address known.
> 
> What's the rationale for this? (i.e. why not always just include
> 127.0.0.1 and ::1 last?)

Because they are an implementation detail I think. If something wants
to know the local IP address, then returning that information is
really useless...

127.0.0.x is really an address we should never present to the user
ever, unless there#s no better way... I mean, I am pretty sure I could
explain a non-technical person off the streat what an IP address is,
but I am pretty sure I'd had quite some trouble explaining what the
purpose of 127.0.0.1 is on top of that...

Lennart

-- 
Lennart Poettering, Red Hat