From: markus schnalke <meillo@marmaro.de>
  To  : <masqmail@marmaro.de>
  Date: Fri, 16 Jul 2010 23:36:27 +0200

Re: [masqmail] 127.0.0.1 vs. localhost (was: What masqmail intends to be)

[2010-07-16 21:56] Juergen Daubert <juergen.daubert@t-online.de>
> On Fri, Jul 16, 2010 at 08:45:42PM +0200, markus schnalke wrote:
> > [2010-07-16 18:20] Juergen Daubert <juergen.daubert@t-online.de>
> > > On Fri, Jul 16, 2010 at 02:26:39PM +0200, markus schnalke wrote:
> > > > [2010-07-16 12:43] Juergen Daubert <juergen.daubert@t-online.de>
> > > > > On Fri, Jul 16, 2010 at 01:05:02AM +0200, markus schnalke wrote:
> > > > > >
> > > > > > Local delivery will be available by default with 0.3.0. Masqmail will
> > > > > > listen on `localhost:25' by default. This would collide with the
> > > > > > --disable-smtp-server option.
> > > > > 
> > > > > Oops, what do you mean with by default? It listen to localhost:25 even
> > > > > if not configured to do so in masqmail.conf with listen_addresses?
> > > > 
> > > > Yes. I'll introduce this with 0.3.0 (if there isn't one who convinces
> > > > me to not do so). The reason is that there are MUAs that submit mail
> > > > only via SMTP to localhost:25. Pine seems to be an example for that.
> > > > Probably Thunderbird too, if it should use the local MTA. By doing
> > > > this change, we have a convenient basic setup that only requires to
> > > > set host_name in masqmail.conf. This is appealing IMO.
> > > 
> > > Hmm, no no no ;) What if I want a setup where masqmail is listening 
> > > only on e.g. 192.168.0.1 but not on 127.0.0.1? 
> > 
> > No problem, set `listen_addresses' to "192.168.0.1:25".
> > 
> > I think we've got our wires crossed (in German: ``aneinander vorbei
> > reden'').
> 
> Indeed :)
> 
> > Everything is still as it was, except:
> > if `listen_addresses' is not included in masqmail.conf, then it is set
> > to "localhost:25".
> 
> Now I get it, that's of course a nice. I thought that your idea was 
> to always listen at localhost:25 regardless of a listen_addresses 
> setting in masqmail.conf. 

Good, we're talking the same language again. ;-)



Now about the localhost vs. 127.0.0.1 question.

I investigated:

Wikipedia writes: ``Localhost always translates to the loopback IP
address 127.0.0.1 in IPv4, [...]''. But you cannot trust Wikipedia...
and indeed, I think they are wrong.

I altered my /etc/hosts to have:

	127.0.0.1       foo
	192.168.0.100   localhost
	192.168.0.74    dream.schnalke.local dream

(192.168.0.74 is the IP address of the machine. 192.168.0.100 is some
different machine.)

Ping gets fooled:

	$ ping localhost
	PING localhost (192.168.0.100) 56(84) bytes of data.
	64 bytes from localhost (192.168.0.100): icmp_req=1 ttl=64 time=2.12 ms
	^C

Dig does not get fooled:

	$ dig +short localhost
	127.0.0.1

Host neither:

	$ host localhost
	localhost.schnalke.local has address 127.0.0.1

The resolvtest test program, that compiles from masqmail's sources
(from 0.3.0 on), does not get fooled neither:

	$ ./resolvtest localhost
	A:                        
	localhost.schnalke.local        127.0.0.1

	MX:

	IP resolved directly (assumed FQDN, no default domain added):
	127.0.0.1

When I tell masqmail to listen on localhost:25:

	$ grep listen_addresses masqmail.conf 
	listen_addresses = "localhost:25"

it cannot. The log writes:

	#  tail -2 /var/log/masqmail/masqmail.log 
	2010-07-16 23:22:00 [11075] masqmail 0.3.0 daemon starting
	2010-07-16 23:22:00 [11075] bind: Cannot assign requested address


Although it seems to be very unlikely that some administrator sets
`localhost' to something other than 127.0.0.1, it is more secure to
default to 127.0.0.1. This IP address is defined in RFCs:

- RFC 1700 (page 5):
    {127, <any>}
    Internal host loopback address.  Should never appear outside
    a host.

- RFC 3330:
    127.0.0.0/8 - This block is assigned for use as the Internet host
    loopback address.  A datagram sent by a higher level protocol to an
    address anywhere within this block should loop back inside the host.
    This is ordinarily implemented using only 127.0.0.1/32 for loopback,
    but no addresses within this block should ever appear on any network
    anywhere [RFC1700, page 5].

In contrast, I found nothing about the `localhost' to 127.0.0.1
mapping.


I'll change the default listen_addresses to "127.0.0.1:25".


meillo