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2 Identical MAC addresses on the same network
Posted: Mon Sep 12, 2005 10:01 am
by ccb056
What happens if:
I clone the MAC address of a PC to another PC or router, both are on the same network, both have the same MAC address at the same time.
?
Posted: Mon Sep 12, 2005 10:17 am
by fliptw
the exact same thing when half the cars on the race track suddenly lose steering control.
Posted: Mon Sep 12, 2005 12:25 pm
by ccb056
The MAC addresses travel the path of least resistance? (in a perfect world, a straight line)
question, are these cars in motion when they loose steering control, because if they are in the pits, nothing would really happen
Posted: Mon Sep 12, 2005 12:37 pm
by Top Wop
That would be impossible since every MAC address in the world is made to be unique. But by the freak chance that it is true then chances are they would continue to work but bandwith would be really slow for those 2 machines. If the router is hooked up to those 2 machines then the router would detect that there are clone mac addresses and may do something about it, like shutting down one or the other or both. In which case its a waste of time since you should just throw out the damn NIC and get a cheap one at Office Max for ten bucks.
Posted: Mon Sep 12, 2005 2:50 pm
by Jeff250
I had a cloned mac address on my router like that at my folks' place. Never really thought about that implication, but I never ran into any problems.
Posted: Mon Sep 12, 2005 2:59 pm
by DCrazy
The cloned MAC only applies to the WAN side of the router. The LAN side still sees the router's original MAC.
Posted: Mon Sep 12, 2005 3:20 pm
by pATCheS
If two machines shared the same MAC address on the same network, packets coming from other devices would be received by both devices. It would be okay as long as only one of the two machines acts on any directed incoming data, but this is not guaranteed anymore since now both machines are receiving the same packets. Now imagine if the machines with identical MACs were both web servers
It'd cause all kinds of errors.
Posted: Sun Sep 18, 2005 10:12 pm
by Capm
Well... If they had different static IP's it may work for some apps, since I believe stuff is routed to the IP address and not the mac address first. And I say static because the same Mac address on DHCP would likely try to pull the same IP
Posted: Sun Sep 18, 2005 10:20 pm
by DCrazy
IP addresses are converted to MAC addresses via ARP (Address Resolution Protocol), which operates on a lower level of the OSI model. The problem would arise in the Ethernet layer, not the IP layer.
IPX/SPX and AppleTalk-over-Ethernet would have the same problem, and there's no IP (much less TCP/IP) involved there anywhere.