Others have given you good answers, but I felt I could share some
insight on the matter..
The MAC address of a NIC is used by switches to send packets out the
right port - As soon as you add a routing element, all traffic to a
routed IP appears to be destined for the router, if one goes by the
MAC address in the packet.
If the destination MAC were to be encoded in the packet, no switches
would be able to keep their internal tables sane, as it would be
flooded with MACs, all on the same port (the one connected to the
gateway).
When a switch recieves a packet adressed to a MAC that doesn't appear
in the switch-internal list, the packet will be flooded (sent out on
all ports). Once a packet from that MAC passes through the switch,
that MAC will be added to the list, and future packets only leave that
one port.
The main function of a switch is to keep irrelevant packets away from
hosts, but packets to unknown (to the switch) hosts get sent
everywhere, just like a Hub would do.
yes - thanks all, it appears its a cross network 'issue'
thanks
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