[CentOS] NMAP - reveal MAC address

Wed May 7 22:21:07 UTC 2008
Tom Brown <tom at ng23.net>

> 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'