Re: notion of a local address [was: Re: ioctl SIOCGIFNETMASK: ip alias

[Wietse Venema]

dean gaudet:
> On Thu, 6 Sep 2001, Wietse Venema wrote:
> 
> > Andrey Savochkin:
> > > > That is not practical. Surely there is an API to find out if an IP
> > > > address connects to the machine itself. If every UNIX system on
> > > > this planet can do it, then surely Linux can do it.
> > >
> > > Let me correct you: you need to recognize not addresses that result in
> > > connecting to the _machine_ itself, but connecting to the same _MTA_.
> >
> > The SMTP RFC requires that user@[ip.address] is correctly recognized
> > as a final destination.  This requires that Linux provides the MTA
> > with information about IP addresses that correspond with INADDR_ANY.
> >
> > I am susprised that it is not possible to ask such information up
> > front (same with netmasks), and that an application has to actually
> > query a complex oracle, again and again, for every IP address.
> 
> how does your MTA figure out that it's behind a NAT?  it doesn't matter
> what unix it's running on, there's no standard way for it to know that an
> address translation has occured before getting to its front-door.

The MTA does not have to know. The DNS on the inside of the NAT
gateway should list "inside" machines by their "inside" address.

That eliminates a lot of other problems as well.

	Wietse