[CentOS] NMAP - reveal MAC address
Tom Brown
tom at ng23.net
Wed May 7 22:21:07 UTC 2008
>
> 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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