IP Address Question

[Dazed_75]

On Feb 11, 2008 11:02 PM, Kevin Brown <kevin_brown at qwest.net> wrote:
> Dazed_75 wrote:
> > I was working on a friend's systems today and saw something I did not
> > understand.  Yes, they were windows boxes, but my question is purely a
> > networking question.  Basically he has a desktop machine with a wired
> > connection to a wireless AP/router (Airport brand I think) and a
> > laptop using a wireless connection to that same router.  The router is
> > providing DHCP Server functionality and serving addresses
> > 192.168.0.100-xxx. All that seems to be working fine.
> >
> > The ethernet adapter in the desktop showed it was operating as
> > 192.168.0.101 with a subnet mask of 255.255.255.0 which I thought
> > meant it would only accept packets addressed to 192.168.0.something
> > and broadcast packets on that same net.  I had also believed that the
> > 4 wired ports on the router were switched, not a hub.  Hence I was
> > quite surprised that the firewall had seen and denied access to a
> > request from the laptop 192.168.0.102 (UDP port 49xxx) to
> > 239.255.255.250 port 3702.
> >
> > Yes, the laptop is a Vista machine and therefore is using their new
> > discovery protocol, but my question is why the desktop software ever
> > even saw this message. I know I am missing something very basic
> > because I would have thought the switch would not even have put the
> > message on the desktop's wire and that even if it did, the ethernet
> > port hardware or driver on the desktop would not have passed the
> > message in to where the firewall would see it.  What am I missing?
>
> What you are seeing is a multicast packet from the system announcing it
> is now on the network.  If you look at your route table you will see a
> default route for 224.0.0.0/240.0.0.0.
>
Thanks guys.  I am sure that must be it.  I don't really understand
"multicast" versus "broadcast" or why it would be done using an IP
outside the range of the LAN.  I can try to learn more about that on
my own sometime.

I sort of know what a route table is but barely.  In linux I do know
how to display one but not in windows.  Seems like you may be talking
about a route table in the router, but I am unclear.  Maybe you could
just clear that up for me.  TIA


-- 
Man is the only animal that laughs and weeps, for he is the only
animal that is struck with the difference between what things are and
what they ought to be.
  - William Hazlitt