RE: Binding to just one network adaptor / ip address?

[Patrick Lidstone \(Personal e-mail\)]

> >I don't want to broadcast xap messages on the wifi or wired
> >interface, just to the loopback device so if I have new mail I'm
not
> >going to send this out to the whole network, just to the
restricted
> >loopback network, but I can't see any way of binding the hub /
> >clients to just one network device.

I don't know the specifics of your setup, but I would add that the
bandwidth used by xAP is miniscule - it is unlikely to adversely affect
the
performance of your wireless network. It certainly has no perceptible
impact on mine, and I run a lot of xAP over it, as well as more time
critical applications such as audio streaming and VoIP.

> How does the loopback interface work? I've not used this
> myself as I just have a very simple one NIC setup here, so
> I'm not sure how you see it installed. Does it give you a
> 'normal' IP address in addition to your WiFi and wired NICs?

The loop back interface/address is 127.x.x.x. All traffic on the
loopback interface never hits the NIC, but is visible within the
local host. It's handy for internal inter-process communication.

> Easiest way to test would be to install Hub or Viewer on
> another PC if possible, and verify that each can or cannot
> see each other on the opposing PCs. Then add in the keys as
> described above and watch the resulting behaviour. I'd expect
> each machine to silent except to itself.

You should be aware of one TCP/IP quirk. Whilst binding to the
loopback interface (or any other network interface) will influence
the interface on which broadcast messages are sent, the tcp protocol
spec is such that it is impossible to identify the source of simple
broadcasts. Thus a multihomed machine (one with multiple interfaces)
will pass xAP messages to the hub irrespective of which NIC they
are seen on. This means that, for example, binding to the loopback
interface doesn't provide any additional security in terms of guarding
against unsolicited messages, and that applications on a host which
can see (multiple) xAP networks on multiple NICs may get a bit
confused.

Patrick