RE: IP ADDRESS OF MACHINE

["Rupert Wood" <me@rupey.net>]

Snodx wrote:

> BUT the interface through which an internet browser like Netscape
> Navigator or Lynx interacts with the Internet HAS to be after all
> one.

No. It will ask the OS for a connection, and the OS will determine which
interface to use from its route table. If you access both an intranet
and an intranet link then NS/Lynx may well use two different local IPs
during one session.

> I am talking about THIS IP Address that the system is using to talk
> to the internet.

The interface which talks to the internet will have:

    * a gateway address configured (which is not also a local address;
      sometimes you'll see interfaces configured with gateway their
      own address or loopback)
    * an unrestrictive routing entry, usually destination address
      0.0.0.0, netmask 0.0.0.0.

I'm not sure if both are necessary (or even sufficient); certainly if
there's only one non-local gateway configured then you use that
interface but if there are multiple then you'll have to check the route
table. Again, I don't know which system calls you'd use to do this on
any platform or if they'd be portable.

There's also no guarantee that the IP on that interface will be exposed
to the internet at all, e.g. the gateway might be a local NAT/firewall.
A browser can even just be targeted at a local web proxy without  any
gateways configured at all.

Rup.