[Guy Harris <gharris@xxxxxxxxx>]

Breen Mullins wrote:

> You're almost certainly connected to a switch (which is marketing-speak
> for a bridge),

Really?  I think of a bridge as a device that forwards all received 
packets to those networks on the bridge, other than the one on which the 
packet came in on, where the links to the networks in question are part 
of the spanning tree of the network, while a switch forwards broadcast 
packets to all ports, multicast packets either to all ports or to ports 
it knows are listening to that multicast address, and unicast packets 
only to the port it knows has an interface with that multicast address 
plugged into it.

But, yes, Ethernet networks tend to be switched, these days, so A, B, 
and C are probably plugged into a switch (perhaps with a router behind 
the switch).

> Some time with Google for the search phrase 'ethernet switch' will help
> with the basics of switches.

And also see

	http://wiki.ethereal.com/CaptureSetup/Ethernet

> The bottom-line answer is that you can't do what you want.

...unless the switch supports "port mirroring" or whatever the vendor 
calls it *AND* he has enough access to the switch to allow him to turn 
his port into a mirrored port - but, even if the switch does support 
that, it's unlikely that he'd get that access; he'd have to ask the 
network administrators for it, and I suspect they wouldn't grant it.